Could he have also banged the other tooth too without realising? My son knocked his front left tooth straight back up into his gumb from a fall, fortunately it grew back into place and didn’t discolour, but the tooth underneath (bottom set) started to go slightly discoloured about a year later and we didn’t even know this had been knocked at the time.
I had this happen to me and had a dead tooth and the dentist told me that the bacteria trapped in it could cause my other teeth to discolor if i did not have a root canal promptly.
My sons front teeth look worse then this.Im going to make a dentist appointment soon but his is from juice.Doesn’t matter how good we brushed it is pretty dead and rotten.Bad teeth runs all in my family though.