Unusually common blunder (how come?)

In bullet, I often plays a transposed version of the Tennison Gambit. I happened to start playing it simply because I was premoving Nf3 after e4, and that doesn't turn out very well if your opponent goes for the Scandinavian. Anyways, I became quite comfortable with the Gambit and started studying it.

After dxe4, I go Ng5, then - if all goes well - place my bishop on c4 threating f7. Most of the times my opponent goes e6, but when they don't, it's a complete winning position.

What I noticed is the unsually high frequency at which my opponents play the move Qd6 in this variant, a fairly huge blunder, below an example. 

I was wondering how come, that even relatively high rated players fall in this and play Qd6 seemingly without realizing that they're giving away their queen for nothing. 

Any ideas?

They might want to attack the bishop on e6 without realizing that the square is defended by the knight?