I actually think what is described there is more of 80:20, than a burnout. The first 80% of a new product are usually quite interesting to work on, but the last 20% of necessary touches are tedious work, that still needs to be done though.

What makes you say this is 80:20? The thing that got him out of the funk was fixing a minor UI issue:

> Once he asked me "Father, what is this thing in the list of things I can order?" ... "This is atomic bomb" .. "Oh, I want to order it" .. "No, we don't even have it researched" .. "But, why is it in the list then, it doesn't make sense" ... "Hmm, you are right, it doesn't, I might actually fix that." So I opened Factorio source code after a long time, and made the change, that the filter and logistic request selections didn't contain things yet to be researched (unless you force-unlock it in the settings). I made a change to Factorio, and it felt good, and I started to want more, this is how I got from the lowest point.

He didn't get back into it because the problem was particularly meaty or interesting to work on. It was a small piece of work that nonetheless allowed him to feel like he had impact. Because he was connecting with someone who was actually engaging with and getting joy from what he was building (and it might have helped that the person was his son).

I guess it's possible that what initially put him into the burnout was working on tedious things that felt like they had no substantial impact (though nothing in the post really indicates that IMO). But, that doesn't mean that this isn't burnout. Burnout is exactly caused by a felt loss of control and/or impact.