You’re right, because of the context, the analogy of the PG Tips monkeys is irrelevant. Here he has portrayed a person who he knows has black heritage as a monkey, and his apology didn’t come across as sincere but rather an attempt at deflection. You can believe whatever you want, he should have known better, it’s not that he thought “I’m going to post something racist”, but that he missed any inherent racism when it is obviously there.

Just imagine yourself in the place of a person with black heritage and someone portrays your child as a monkey and says “ I didn’t mean anything by it, just a bit of a joke, cos’ I’m not racist you see”