I think there is nothing inherently wrong with changing code that can be improved but shouldn’t have focus as long as the other work also happens. It improves his understanding of the codebase and makes the code “better”. (Obviously, feedback needs to be taken into account.)

I can think of two reasons why he worked that way:

1. It was unclear exactly what he should be focussing on. Were there tasks/tickets describing what needed to be done? Or was it just a vague “fix this”. Doing peephole, local changes to code are easier and improve understanding of the whole. 2. In addition to working on the main tasks, I tend to fiddle around with other code while the main problem is percolating in my brain. Somehow working on other problems helps me solve my main problem faster than just focussing on the main goal.