I really dont care about swearing. I think it's more about what they're saying, shit head vs poo head, is one ok and one not? Who decided which words are swear words and which aren't? (It was the church btw).
I think it's better to teach him that there will people around you who say things you dont like, who speak differently to you and that's none of your business. If he tells you to fuck off then you dont need to accept that, but no one is too precious to hear the work fuck and if you go around the world feeling you have the right to censor people based on your own choice of language then you're the problem and will get yourself in alot of arguments with strangers.
For me it's about, what is the message they're trying to convey, is it acceptable? You can say abhorrent things without swearing. You can be racist, homophobic and be offended by the word shit, that doesn't make you the better person.
Go away vs fuck off, means the same thing, one is more emotional. It's more important that kid is taught to control their emotions and not be mean, rather than dont say the work fuck or shit.
Also, not particularly relevant, it may be autism related, I'm autistic I follow rules I believe in fiercely but not those I dont understand, uniform policies at school are irrelevant and i never followed it. I feel the same about the idea that certain words are swear words despite meaning the same thing as non swear words so I dont follow it.