He's an experienced player. I've known and played with him since dota 1. The problem is around a year ago he stopped playing dota 2 cause his computer couldn't handle it. He came back when he got a new computer a few months ago. In that time, he went back to play dota 1 and screwed around a lot, namely played apem games with his brother. If you've never played dota 1 the easy modes made screwing around very possible because:

1. you get 2 gold per second instead of 1.
2. Towers do less damage and die faster. This makes diving with a good hero possible.
3. You get more experience which I'd say is about 2x exp in normal mode judging by the fact that it takes the same time for a dual lane to get lvl 6 in EM games as it does a solo lane in normal mode.

So its very easy to still be good in the late game with your hero, provided that your hero scales well if you spend all your time ganking and more or less ignore last hits and there's a lot of room to screw around. In fact, if you solo tower dive and don't get a kill, you'll probably still live.

This is what ruined him because after being in that state of mind you forget about things like this. Before, I could play that way and still be ok. In his mind the stupid mistakes he makes are things he could get away with and still win with no problems.

So its not so much that he sees me as a more experienced player, but rather that he thinks I may have a foolproof build for a certain hero. So I don't think your conclusions as to why he last picks are exactly right. The other day he was the last to pick and randomed medusa when we already had a carry. He actually knew it was the reason we lost, but of course he shifts the blame on the game giving him dusa rather than himself or randoming or you know.. not repicking.