Wonder if anyone can shed light on our recent experience with infant seatbelts and Thai Airways?

We recently completed a family trip BOM-BKK-HKT-BKK-BOM on TG, the party comprising me, Mrs EB, Miss EB and Master EB. Our youngest, Master EB, is 14 months and so we didn't buy a seat for him, electing to travel with him on our laps (we were in J). On boarding I asked the crew for an infant seatbelt and they were hesitant about giving one out, and explained that it was better to hold Master EB tightly on our laps instead. I insisted on the seatbelt and they handed it over. This same discussion happened on each of the 4 flights when I asked for the extension seatbelt, and the Purser on the last sector BKK to BOM was very insistent about it being against FAA(?) regulations to use them, but ultimately our own choice.

We travel reasonably frequently as a family, most often with BA but also some travel with Jet in India and SQ, and have never had this experience before; instead the airlines (esp. BA) have insisted that we use the extension seatbelt. Assuming that the TG Purser meant the American FAA, do they (the FAA) genuinely recommend that if you're not using an infant seat that you don't use an extension seatbelt for the infant but just to hold them? Or were we somehow at cross-purposes?