Why is this a blunder?

I analysed this trap I developed for the Englund's Gambit and lichess.org says that this move is a blunder but chess.com says that this is an inaccuracy...

[lichess.org analysis]

[chess.com analysis]

Move classifications are based on the change in evaluation. How that evaluation change is classified, is a subjective call but can also hinge in a pretty minor difference in that eval.

It can also differ on the same site if the engine version is different or at a different depth/strength

Thanks for your explanation. I'm pretty new to the 1.d4 openings that's why I just wanted to be sure...

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5 Nc3? is a mistake: turns a won position into a drawn position.

5 Bd2 is winning for white.

5 Nc3 Qxf4 6 Nd5 Qe4 7 Nxc7+ Kd8 8 Nxa8 Nxe5 should draw.

chess.com gives move classifications based on win rate, but lichess gives classifications in another way

https://support.chess.com/article/2965-how-are-moves-classified-what-is-a-blunder-or-brilliant-and-etc

That article is almost 2 years old. It's probably seriously out of date by now.