The more nervous and tense he gets, the more likely he is to do it. That much is like any condition - gets worse with stress. He was very likely to call them that again if he tried to apologize to their faces. He literally cannot control it. He used to try to use a kind of...gag, but even that didn't work, he'd just spit it out. He was knighted by Queen Elizabeth and AS she was knighting him, he said "**** the Queen." He's had to have his dog specially trained to basically not listen to certain commands, because if they're at a railroad crossing, he'll tell the dog to run across the tracks if a train is coming. He doesn't want to kill his dog, that's how bad this is.
I think he could have crafted a better written apology though, with more awareness of the weight that word carried, especially to Americans, which MBJ is. People in the UK are very used to his story, but the world is not necessarily as familiar with it, and right now, unfortunately, the world heard it because the BBC is apparently run by idiots. I know he's spent his entire life apologizing to everyone around him and he's trying to destigmatize the condition, but I don't think this is the moment to wave that flag especially high, and I'm not sure he fully appreciates that at the moment. My only thing is stressing he truly cannot control it, and he definitely has coprolalia.