Wow, in all my years I don't think I've ever seen it like this...probably between delayed flights, heavy arrival day/time, not staffed because its "officially low season" and/or computer problems - I'm going to go out on a limb here and say this is not an every day occurence!
As far as airline staff being woefully mis-informed about Jamaican immigration and customs - when the forms changed (became both immigration and customs on one form) I had a flight attendant insist that we only needed one form. I had to argue, beg, plead and cojole for another form because I knew for certain that we each needed an immigration form and could fill out one custom form (the back of an immigration form). I think it sucks that airline personnel are not trained in that manner but I was NOT going to let it go, knowing better. Besides - logic says each passenger needs an immigration form, no? Sometimes you get a flight attendant that's tired, having a bad day or just stubborn. Don't let it go - get as many forms as you need.