Well, while I'm certain he was exaggerating, most every American history textbook I've had throughout school, various internet articles (including Wikipedia, though we all know about that), as well as...Revolutionaries, by Jack Rakove? I can't remember if it was mentioned in that or another book whose name I can't quite recall, have led me to believe that the Scotch-Irish were adamantly Patriot.
Could it be maybe that we're having a failure of communication and are talking about two different things? While I have no idea if this is the case, it wouldn't surprise me if more recent Scots-Irish immigrants were loyalists, while the older, more entrenched ones were the ones whom were Patriots. I'm basing this entirely off my own reasoning and I wouldn't be surprised if I was making no coherent sense at all.