I'd be more worried if you weren't bothered by what you saw. You reacted normally, and quite possibly saved his life.
Something similar happened to me one day, except that it was in a busy street. Old geezer topples backwards with a very audible crack, and people just walked past him like he didn't exist, or worse - stood there giggling.
I've witnessed and had to deal with more than my fair share of medical emergencies. Apparently I am very useful in a crisis, others describe me as cool and quick-thinking. This may be a benefit of Asperger's - enabling me to operate in the here-and-now without emotion or revulsion - but it comes at a cost. Afterwards, when I've had time to properly analyse what has just happened, it isn't uncommon for me to break down in some way and I'll either sob or completely lose my temper. The emotional fall-out is an order of magnitude worse if the afflicted person is a child, or someone I know.