There are no words for the WTF about the whole thing. I mean, I just did a little more digging, and it turns out that other sources list the Pownoll birth date as 1786, not 1776 as Wiki had been, so it looks like he was legitimate and from the official Pellew homepage on the "Bastard":

* His actual legal name. The middle name was a tribute to a Mr. Bastard, who was present at his christening. The bowl of cheer must have been flowing."

*is in hysterics* This teaches me to jump to conclusions/rely on Wiki to much.