When a user 'action' (in a general sense) is executed in Salesforce, assuming no callouts or async jobs are executed, isn't the code running in a single thread/transaction? Assuming so, how is it that I get a row lock error when I know I'm the only user in my personal sandbox (no other user is awaiting for the same record I'm updating). Based on this link: https://help.salesforce.com/s/articleView?id=000387767&type=1, it's possible to get a row lock error if there are thousands of child records. However, it does mention again if there are multiple users.
I ended up queueing the part of the code that was throwing the row lock error and the issue went away. However, I'm still confused per my query above.