Well, the thing is that most Crowntails are Delta-tail based. Meaning that the Crowntail gene is entirely separate from the Delta-tail gene, but, due to selective breeding, they usually are paired together. You can also have a Veiltail Crowntail, or a Plakat Crowntail, but they are not often bred for, so most of our Crowntails are Deltas with Crowntail trait.
Halfmoons are based off of Delta tails in that, in order to get a Halfmoon, you have to have Deltas. But Crowntail trait is independent of tail types. It is entirely possible that your boy has the spread of an HM. Whether he has the Crowntail gene or not (and he OBVIOUSLY does) is irrelevant in determining the Halfmoon spread.
If his tail opens up to an entire 180 degree spread, then he's a Halfmoon. A true Halfmoon is somewhat rare, however, so it's possible he's just a Super Delta, which, I believe are those that have a tail spread of 150-179 degrees.