Analysis says I made the only blunder, and more mistakes... but I won

If my opponent didn't blunder, how did they get into that position (especially against a much lower-ranked player like myself)?

What position do you mean?

And what kind of feedback do you actually want?

Sorry, I'm new to analysis tools so it just seems odd that moves 20-22 he hasn't made any blunders, as to my limited brain that's where the game turned.

19 . . . nxb6 is better.

23 . . . ba6 is a mistake. Leaves q and n hanging.

After 26 rxd7 it's all over.

Basically chess com's free analysis is not very reliable, software at low ply. 

There wasn't much justification in e6 really,  and you were quite lucky in opponent allowing knight into f7 as mentioned.

Basically, Chess.com deliberately hobbles the free analysis as a way of selling its memberships.  The free site Lichess.com provides vastly better free analysis, so its obvious that the vastly better funded Chess.com could provide quality analysis to everyone if they wished.  

Thanks for the comments, especially taking the time to annotate the game asmundto. I hadn't realised the free analysis tool was less good than the paid version.

I started the game not knowing the opponent's opening (my chess was learned as a young kid and openings simply weren't taught) so I was making it up as I went along!

I partially went e5 because I didn't see what else to do, partly because I like going offensive, and partly because thought ending up with my pawn on that square on move 8 blocked the opponent in a bit by controlling those squares...?

Thanks for the advice, appreciated.