How is this not checkmate?

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u12345432100

My opponent resigned after this, but I'm not sure why it isn't checkmate.  I honestly can't figure it out.  Thanks.

notmtwain

He can take your b pawn en passant.

u12345432100

Ohhhh, thanks!

s2t2u2p2
notmtwain wrote:

He can take your b pawn en passant.

OGM. I read " he can take your b pawn, peasant"

I was like "Wow, what a dk."

Sulle

hahah s2t2u2p2 !