And they likely had them on site there too. Acknowledging that this is a horrific event for all involved - give the people on site there a little break. The circumstances were unusual and track meets are a three ring circus to begin with - I would be surprised if they did not respond quickly considering the circumstances. I also expect that they would have stopped the race if that in any way was hindering him getting proper treatment. Hopefully this turns out to be just a very scary incident without long term consequences. However, it does seem silly to me for anyone to make any medical diagnosis based on tweets and what little video footage there was.
In addition, identifying the seriousness of the event by the first people to reach him would be difficult. First of all, it's completely unexpected for fit athletes to have what appear to be a cardiac event during a race and secondly, it appeared as if he fell initially.