Hmmmm.    That doesnt’ sound good.   Rabbits get something called rabbit syphillis.   It gets crusty.  Not passable from pets to humans.  Not quite the same thing. 

Rabbits can get herpes.  It can be passed from birth.     Syph is scabby  and crusty there are some pics of rabbits with it. Thats how i know. 

I would have the vet check it out just in case it is something to be treated.   Or as you read it may be nothing.   You said it is white.  I don’t think rabbit syp or herpes is white. 

It’s description reminds me of a pimple.   My dad used to get those white things.  Over his eyelids and stuff.  They were nothing I forget the name of them tho.   My hubby has a few things  on his upper arm.    Like a little white flap of skin.   Real small and painless.

Probably made you think what the hay   with the first 2 things I mentioned lol    Not to worry probably the skin flap things. 

Does it sort of look like a little whitehead?   It is probably nothing.

I do not know about this as a normal bump.

There are sores that a rabbit can get  (what BT referred to).  Look up rabbit syphillis/vent disease which can eventually transfer to mouth area too.  IF this is what it is it is very treatable. My very first bunny had this

Do you notice any of these same sores on his lips?

I would have him checked out by your vet. It might be nothing, but it might be something…

I tried researching white bumps, but I couldn’t find anything that inferred that it is just a standard thing, did you find that information online? Or was it from the vet? I’m not that experienced with medical issues myself, so I can only advise that if it were me, I’d keep an eye on it for about a day or two and if it hasn’t improved or gotten any better I would go to the vet.