I saw this position after having a look at the King's Head opening (C20), which was mentioned in a thread I was reading. All I can say is that Erik was brilliant to foresee this turn of events, I wouldn't have even considered it.

Bf5 is a thing of beauty.

the rook could then checkmate!

One should always consider this kind of forcing sequences since knight and rook are almost as strong as Queen. In certain positions it's even possible to sacrifice Queen for a knight, rook and some positional compensation. However, here the rook gets captured with chek and black king doesn't have too many defenders which often indicates that there might be some tactics. Quiet little moves like Bf5 in the middle of sacrificial attack often create even stronger impression than the sacrifices itself.

Why on earth did Black resign?

nicely done!

 Next comes Rg1 mate which cannot be prevented