In the presence of scopalamine alcaloids there would be no changes to his pupil size when light is introduced. That was the specific question I asked the doctor. Jacek's pupils are responding so they believe it to be that, being alone, drinking by himself, he had a viscous purge reaction and at some point, in order to get air, he gasped and his lungs pulled in his expulsion. Bad timing, to say the least.
This is one of the reasons why it's probably best to refrain from eating for hours before ceremony. Vomiting is one thing but regurgitation is another entirely, it involves the food you have previously eaten and this can be avoided if you're dieting before you're in ceremony.
And it also points out another very important aspect to ceremony. Unless you are very experienced, you should never do this alone. There is a reason why people come to ayahuasqueros. I know that Jacek was very experienced and he had a very unfortunate accident, this would not have happened had there been someone there, experienced with what to do in this situation when someone needed assistance.
I am not saying that Jacek had a meal before ceremony, just explaining things in general.