I don't think it's a valid question. Since you can't really find out in-game, unless you actually try the contrived combo -- and even then you'd have to do it a few times in a few different ways to be sure. You can't just do it once and assume that answer is always correct, since there might be other factors.
Even the wiki can't tell, since the exact algorithm is not known. I'm not even sure how the person who asked the question can know because it might depend on factors other than the skill increases. Race was mentioned above. Maybe birthsign factors into it. Maybe the speed at which you complete the tutorial. Or how much loot you are carrying. Etc.
From the discussion page of the wiki:
the code for which is hardwired into the game so it's not possible to see how exactly the selection is done.
http://www.uesp.net/wiki/Oblivion_talk:Escape_From_Prison#when_baurus_suggests_a_class..
... I went through with a imperial and did what you said and only used blade, destruction and sneak and He thought i was a pilgrm. so thats my answer....
Which is interesting since a Pilgrim does not have any of Blade, Destruction, or Sneak as majors.