But why did the third guy immediately recognize the problem (and put in place a very effective solution) without being prompted? Was that a "skill" he learned in a programming class?
It might have been that he was just a clever guy, but let me offer an alternate possibility -- the new guy recognized the problem precisely because he was the new guy.
Specifically, it's common for people not to think about minor annoyances they have grown used to. It's the boiling-frog effect -- a programmer who has been working on that app every day since the very beginning, as more image assets were slowly added, might not notice the gradual slowdown of the app's startup phase, because at first it was fast enough, and eventually he/she just got used to the slow startup because "that's just how it is with this program".
The new guy, OTOH, sits down with the app and because he's had little or no previous experience with the delay, finds himself noticeably annoyed and says to himself, "that is a problem... maybe I can find a way to improve that".
tl;dr -- a person with fresh eyes can often see problems that the old hands have grown too accustomed to, to notice.