Dillard said he was in the plaza for 2-3 minutes(can't remember the source, may even be the WC but not sure).
Anyway Foster's in the shock zone, she saw it from close range, terrible. Might have effected her recollection some, it has been known to.
That said, I think the limo clearly slows and Greer most likely tapped the brakes, it's no biggie, stuff happens, If I'd blame anyone it would be Rowley.
There's an automatic assumption that if he did tap the brakes then that suggests guilt, LNT's feel it too, that's why they get their panties in a twist over it, one of the few things we all agree on perhaps, is that it just doesn't look good if he did.