Yes, it looked very very strange! I'm also really surprised no one seems to talk about it. It looked a bit suspicious because it was exactly at the 30km-mark. And I did not see him throwing up, just standing there with some guys next to him, but no throwing up, nothing that actually indicated major issiues. I can't believe he would drop out of a race like this unless it was something serious... but what could it be... Isn't there a post-race an interview with him? Or a reaction from hos coach/manager?
He did throw up. It was shown later - and Kitwara even pulls him away from the parked bike.
And if he was not feeling good then it made perfect sense to drop out at a water station where he could more easily get help/support.
But I think that what did it was seeing Kitwara stop. Kipsang wasn't feeling good already and there he had the support of the pacer ending and the opportunity to end his own discomfort.