Is this a real move?

I played a game where I was probably going to loose anyway, but then my opponent made a move I have no idea you could make. I resigned.

I went to c4 and then he took my pawn (c4) with his pawn (d4)

"19. c4 dxc3"

The log claims he took c3 but I put my pawn on c4...

Is this a bug or a new move I've never heard about? (I'm a beginner)

Proof:

Hello Collaide! It's a new move for you   It's written in the rules of chess, under the section "en passant rule"

Thanks for the info, I'll look it up!

the server just got overloaded and i was bumped from a game i was winning.  now i'm back on and it says that i lost. 

well, he may have actually had a piece advantage but i was still in the game.  anyway, why do i get a loss if the server was overloaded?

I also lost a game due to a crash, *smh*

why does that happen?