chess analysis is wrong?

hello,  just playing around with some of the free chess lessons on the site, and noticed this odd suggestion when doing the two - knight checkmate..

now if i click the hint button it tells me to move knight to b2, and when doing so it comes up with a pop-up saying "knight to b2 was the best move" ...

(in this photo i have clicked on the hint button and its highlighting it wants me to move knight from d1 to b2).

In this screenshot i moved knight from d1 to b2, with the popup in the bottom right saying "excellent move, the best move was Nb2) .. and as you can see the AI moved the king to a1? 

Am i stupid and missing something obvious or is the analysis program not very good? What's going on? I am curious to know how much I should listen to the analysis program if it has seemingly blatant errors?) .. that's of course if I have not forgotten some rule that prevents the king from taking the knight??

cheers 

Two knights can't mate a king without its help.

It is no surprise you get screwy results.

(Taking the pawn was a mistake. You need it to prevent stalemate.)