Well I'm glad your OK and that the helmet did its job.
Regarding your helmet with that exposed foam that cracked, well it was going to crack even in the lightest of impacts because exposed foam just has NO strength at all which is why I'm not a fan of that paticular design. I had a LG ( I cant spell) helmet crack in the same spot when I fell from stationary and lightly banged my head and I'm glad that I had the helmet on but it was a bit lame that it cracked.
I reccomend looking for a new helmet that has the shell completely covering the foam. There's a few around and I think Bell has a commuter/touring helmet that looks pretty sturdy. I'm a fan of Catlike helmets because they are completely covered.
Regards, Anthony