function returning true yet should be returning false? Python method

Question

class ClassicTicTacToe:
    def __init__(self):
        '''
        Initializes an empty Numerical Tic Tac Toe board.
        Inputs: none
        Returns: None
        '''       
        self.board = [] # list of lists, where each internal list represents a row
        self.size = 3   # number of columns and rows of board

        # populate the empty squares in board with empty string
        for i in range(self.size):
            row = []
            for j in range(self.size):
                row.append(' ')
            self.board.append(row)
        #print(self.board)


    def drawBoard(self):

        l1='    0   1   2'
        l2=' 0  %s | %s | %s' % (self.board[0][0],self.board[0][1],self.board[0][2])
        l3='   '+'-'*11
        l4=' 1  %s | %s | %s' % (self.board[1][0],self.board[1][1],self.board[1][2])
        l5=l3
        l6=' 2  %s | %s | %s' % (self.board[2][0],self.board[2][1],self.board[2][2])


        print(l1,l2,l3,l4,l5,l6,sep='\n')

        '''
        Displays the current state of the board, formatted with column and row 
        indicies shown.
        Inputs: none
        Returns: None
        '''





    def squareIsEmpty(self, row, col):

        if self.board[row][col]==' ':
            return True
        else:
            return False


        '''
        Checks if a given square is empty, or if it already contains a number 
        greater than 0.
        Inputs:
           row (int) - row index of square to check
           col (int) - column index of square to check
        Returns: True if square is empty; False otherwise
        '''



    # mark is a string for the users input of x or o
    def update(self, row, col, mark):


        if self.squareIsEmpty(row,col)==True:
            self.board[row][col]=mark.lower()

            return True

        if self.squareIsEmpty(row,col)==False:

            return False
        '''
        Assigns the integer, num, to the board at the provided row and column, 
        but only if that square is empty.
        Inputs:
           row (int) - row index of square to update
           col (int) - column index of square to update
           num (string) - entry to place in square
        Returns: True if attempted update was successful; False otherwise
        '''




    def boardFull(self):
        '''
        Checks if the board has any remaining empty squares.
        Inputs: none
        Returns: True if the board has no empty squares (full); False otherwise
        '''
        nonempty_list=[]
        # TO DO: delete pass and complete method
        for i in self.board:
            # alternatively this could be range(len(self.board))
            for j in range(0,3):
                if i[j]!=' ':
                    nonempty_list.append(i[j])


        if len(nonempty_list)<self.size**2:
            return False
        return True


    def isWinner(self):


        for i in range(len(self.board)):
            if self.board[i][0]+self.board[i][1]+self.board[i][2]==(3*'x') or (3*'o'):
                #return self.board[i][0]+self.board[i][1]+self.board[i][2]
                return True
            if self.board[0][i]+self.board[1][i]+self.board[2][i]==(3*'x') or (3*'o'):
                #return self.board[0][i]+self.board[1][i]+self.board[2][i]
                return True

        if self.board[0][0]+self.board[2][2]+self.board[1][1]==(3*'x') or (3*'o'):
            #return self.board[0][0]+self.board[2][2]+self.board[1][1]
            return True
        if self.board[0][2]+self.board[2][0]+self.board[1][1]==(3*'x') or (3*'o'):
            #return self.board[0][2]+self.board[2][0]+self.board[1][1]
            return True



        return False
    def isNum(self):
        if self.choice=='num':
            return False
        else:
            return True
        '''
        Checks whether the current player has just made a winning move.  In order
        to win, the player must have just completed a line (of 3 squares) that 
        adds up to 15. That line can be horizontal, vertical, or diagonal.
        Inputs: none
        Returns: True if current player has won with their most recent move; 
                 False otherwise
        '''


if __name__ == "__main__":
    new_game=ClassicTicTacToe()

    new_game.update(1,1,'x')
    new_game.update(2,0,'x')
    new_game.update(0,0,'x')
    new_game.drawBoard()


    print(new_game.isWinner())

Creating a version of classic tic Tac Toe with X's and O's. The method isWin checks if we have any win conditions (3 in a row of either x or o) and if we have any it returns true if not it returns false. I've set up a scenario in which it should return False yet it returns True can anyone find why? I'm not sure what the issue is