Men can get depressed after (post) the birth (natal) of their child. Silly to claim that depression caused by such a specific event can't be labelled accurately as post-natal. I've never seen a definition of PND that claims it is solely based on hormones. Mine wasn't.
Personally, I think my labour was MUCH harder on dh than on me. We been through 3 miscarriages together, each one had taken 9-11 months to happen in the first place, lots of other stuff and then he had to stand by me as I was induced for 5.5 days, 3 of them with powerful contractions every 10-20mins. Yet I made no progress except get more and more tired and frustrated, then the waters broke, full of meconium, got an epidural that didn't work at all, the anaesthetist resited it and told us that was risky and that he wouldn't do anything else, even if I needed a caesarean (which was looking more likely by then). Then there were fears over the baby's heart-rate decelerating, then pushing could not get over the final hurdle, then had a ventouse delivery, then all the 6 medical people in the room go into focused action as the cord was tightly round our son's neck. For me, I experienced it all and it was hard, but it was my body and I was more instinctively involved. He thought he was going to lose us both. He was absolutely terrified. 2 weeks later it hit him and he was diagnosed with PND.
Calling it PND doesn't make it an excuse for anything.