Hey, Presto.
This is the hassle with "RP gods VS evil munchkins" debates: it's impossible to generalise.
Choosing a juicy mechanical benefit and using your imagination to fold it coherently into the character is good roleplaying. That's very different from exploiting every loophole you can find, then working up a perfunctory backstory so it holds together.
The PC you describe is growing and sticking with his background. It's a fine use of story and mechanics. On the other hand, I've seen all sorts of thri-kreen monks and teifling hexblades which were, essentially, built as wargame units for their numerical benefits, with characterisation as an afterthought.