Well, it had to be some blood thinner stuff, blood thinning either as a primary mode of action or as a secondary. Something particularly exotic along the lines of snake poison it cannot be for purely logistic reasons, and besides, these are for injection, not digestion.
And BTW, mass onset only indicates that the victims likely consumed the stuff at, or about, the same time. Nowhere is it following from that they had to consume it with their meal 2 hrs before the symptoms - given the Ramadan fast, they could have eaten it the evening before.
That's a good point. I was wondering if it was just a coincidence that they became ill at this meal.
Oral ingestion is also a problem - slows down the effects. So, it may have been administered previous to that meal.