Caro-Kann Defense, Advance Variation, Mitchell version (my version)

Indeed. Nice game. For your level at least. But yeah, I'm also an avid CK player too who disagrees with f4 at any point in the opening. Granted, it LQQKS like a "cool" move (on the white-side)but truth-to-tell it's not black who has to be wary. As it is, keep on keeping on my friend. I suppose you will go far in chess if your attitude & bravado are in sync. Otherwise, i would advise you to be humble and take in whatever advice you can get. Best wishes 😉

4.f4 gains space, reinforces white pawn chain and prepares the attacking move f5.  Maybe not the best move, but certainly an interesting one.

Another reason for f4 is an eventual attack on the kingside which I was preparing to do. That was another reason why I did f4.