Hmm unless you were there I am not sure what basis you have to implicate that the original poster was exaggerating. Did you actually read the original post? Just to help you infestation is defined as “the presence of an unusually large number of insects or animals in a place, typically so as to cause damage or disease.”
The op states he suffered multiple bites on the head, neck, hand and abdomen. The cabin crew reported that he saw a LOT of them on the seat and the op was moved to another seat. The cabin crew also filed an onboard report about the bugs. All of these seem to point to a serious issue which corroborate the use of the infestation word.