When I think about it again I cannot judge whether or not he had a dive reflex but he described being out of breath and very uncomfortable.
Actually, you can often have a very strong DR and feel quite uncomfortable in the same time. If you browse the forum for discussions about FRC diving (where the DR is strongly pronounced), you can see that the feeling of discomfort may often come earlier in the dive and be stronger than at normal dives. Despite it, you'll be able to stay longer and surface safer and with clearer head. So if someone does not want to repeat freediving experience because of discomfort, it is certainly not because of missing DR, but rather because of some kind of phobia, or because he was under too much stress, or simply did not find it interesting. I think the best for beginners is starting with more or less surface snorkeling in shallow waters, and only once they are pretty comfortable and enjoy it, they should slowly start diving. At the beginning just for couple of seconds into small depth, without experiencing discomfort, and then working through to longer times and bigger depth.
However, at beginners, the times and the depth should never be the focus. The focus should be purely on enjoyment, and perhaps on the technique (as long as it does not disturb the enjoyment). Hence, select a protected location with shallow water, with rich flora and fauna, and have the beginners enjoying the view mostly from surface. Only show them simple technique tricks and safety tips (immersion, fin kick, equalizing, surface intervals, keeping quiet and relaxed between dives without wildly swimming there and back, avoiding hyperventilation,...) only when you see they are feeling well in water, and with their equipment, and do indeed listen to you instead of fighting their phobia (or equipment).
