I think it has to do with the type of omegaverse this is. Each story involving omegaverse may slightly (or hugely) change the 'standard rules' or 'stereotypes we expect' in omegaverse. In most omegaverses I've seen, a male alpha cannot get pregnant. This omegaverse, in particular, is a rarity where ANYONE can get pregnant (but depending on the sub gender it changes the likelihood of pregnancy; such as alpha it's hard to get pregnant, omega it's really easy, beta is normal, etc). Also, some omegaverses have their own anatomy present, if you read the webtoon, "Omega Leadernim" the author explains how her omegaverse works in her story, the anatomy of each sub gender/sex, and pheromones.
The stereotypes for omegaverse tend to change depending on if they're a Japnese Manga, Korean Manhwa, Chinese Webtoon, etc.
Hopefully this explains it!
A male alpha can get pregnant?