So my opponent played this odd opening as black. Did I take advantage of it correctly?

I think lichess called it the Great Snake Variation of the English Opening. I'm leaning toward calling it the not-so-great snake variation...
But anyway, what do you think?

as an amateur I would say his approach is very messy and you have control of the centre even before he gives away the pawn when he didn't have to in move 13. When that happened there was no way back into it for him really

Great Snake is 1.c4 g6 and fully playable.

@savagechess2k
That is fully playable. I thought that the GSV was the whole g6 e6 c6 a6 thing, which is playable, but not easy.

Of course 1 c4 g6 is playable, but this whole ...g6, ...e6, ...c6, ...a6, ...b5 thing is bad and gives white a decisive advantage: better development and control of the centre.

Overall, you definitely played a better game than your opponent. My impression of this game is that you had several opportunities to improve. Consider, for example, the move 9. Bd2. I don't like this move very much because black is likely wanting to play Ba6 to trade off your light-squared bishop. If you play another developing move, you reserve the right to play another move after black develops Ba6 because you can always capture back with your queen and improve your queen position at the same time. One of the major mantras of chess is developing your pieces. If your opponent is playing badly, consider delaying development in some cases to punish your opponent. Consider the major weakness of black. By playing in this fashion he is allowing you to develop your pieces in such a way to create permanent dark-squared weaknesses in his camp. For example, one consideration that I have is possibly playing e5. This creates a major hole on e6. Imagine your knight hopping into that square.

There are several moves which I would have never considered. Consider, for example 16. Rfb1. Why not Rfc1? Your pawn on b4 is already well-defended. And actually if you are trying to support a pawn push to b5, you already have that option because the black queen is pinned to the pawn (cxb5?? Qxc7!). Just a few thoughts.

edit:
If I had a recommendation for you, overall, from a broad perspective, I would condense it to this. Try to avoid losing tempos. Focus on developing efficiently. Part of launching a great attack is not losing the initiative. That can allow your opponent back into the game.

I think your opponent blundered left, right and center.