Compilation error for the same statement?

Question

When this code is executed, I get a compile time error -

byte b = 50;
b = b * 2;

Error -

incompatible types: possible lossy conversion from int to bye

I am aware of the fact that Java automatically promotes byte to int during compilation.

Then why does the following code doesn't produce any error and runs fine -

byte b = 50;
b *= 2;

Isn't b = b * 2 and b *= 2 the same?