Batching things into 'contexts' is the premise of Getting Things Done by David Allen. It was popular in the early 2000s. My guess is that the older engineer that told the author to batch things was referencing it [1]. It's a business book based on aggressively making and prioritizing todo lists and then working on them in contexts like 'email', 'phone calls', etc.

[1] https://en.wikipedia.org/wiki/Getting_Things_Done