4.Be6 is a weird move for a few reasons:
(1) You're blocking a central pawn which isn't always bad but should always be done with caution (like a knight on the rim)
(2) F7 isn't falling. There's no direct threat, Nxf7 looks ridiculous, and you can defend it by castling or by moving the e pawn and allowing the queen to help
(3) There are other moves that black wants to play. 4...g6 5.d4 Bg7 6.Qe2 O-O looks solid for black....I'm not checking with an engine and don't play the Pirc, so feel free to say "Uh, mate in 2, sister", but it seems fine
(4) The bishop goes to f5 on move 6, a better square. Obviously you had some second thought about this piece placement
I analyzed the rest of the game. I hope this helps:
So, here was an interesting game I recently had.
I think the lesson learned for me is not to blindly follow a checkmate dream without fully preparing. I think that is what my opponent was trying to achieve here.
I had thought I was going to play a Pirc and it is a testament to the progress I've made in my year of really trying to learn this foolish game that I didn't blindly follow my opening Pirc moves but reacted to the threat.
I'm not sure why 4...Be6 is seen as so bad by the engines. Nor why 9...nd5 was similarly poorly thought of by the engines. Although I understand by Bg4 was a mistake. 9. f3 would have screwed my plans quite a bit.
In the end, I got lucky by an opponent who seemed to have got fixated on his original quick-mate plans. I'm sure he's a good player with a disappointing game. That was more the reason for my win than any brilliant play by myself. It's just nice to be on this side of that conversation.