The post only said after the reset, not that you’d be able to play an entire season before D2:R released.
Personally I think they were aiming for a June release and delayed it because of how badly delayed WoW 9.1 is. If they released at the end of June, it may collide or be very close to 9.1 release and they probably didn’t want D2:R and 9.1 to compete, especially given how few people even log into retail WoW anymore as it is.