If it was started in March it may have done the equivalent of a "12/12 from seed" grow, where it matured while the days were short enough that it went straight into flower. Where you appear to have gotten really lucky, is that as the days got longer it does not appear to have gone back into veg. If it finishes flowering in full hot summer sun, you could get some really nice buds from it. If you start to get odd looking leaf formations, then it's gone back into veg. Keep an eye on it. Best of luck to you.