It's a known fact that gifted children challenge (sic) authority and generally do find nursery difficult
No it isn't. Most highly able children I know of are very keen to please and want to do well.
Reading/knowing alphabet early just really shows what interests them. My oldest won a story competition when she wasn't quite 3yo. Still amuses me that one! Yes, she wrote it all herself, I had no input at all other than posting it.
She was interested in letters (and then numbers) and words, so she played using them. She didn't know her colours, which didn't interest her, until way past the age most children knew them.
Reading age of 5-7 aged 4yo is good, but not amazing, both my dc's forms had 3-4 children at that standard or beyond. Some of those dc have stayed at the top end, some now are fairly average.
Don't label him at this point, it really won't help him.
The best thing you can do to help him is back up his teachers-if he's naughty, he's naughty, not showing how bright he is, and help him with the things he finds difficult-the socialising and that sort of thing. You won't do him any favours if you just put everything down to him being bright.