...when people say "I use X fingers to hold this" and do not explicitly mention the thumb, they're including it in the count. Well, at least I am; I guess OP might be using one more finger than I'd thought. IG the unambiguous thing to do is say "digits" instead of "fingers" when that is intended; mea culpa (though if OP truly meant fingers and not digits their grip is more cursed than I'd imagined).

It sounds like you and I use much the same pencil grip.