For all our complaining that trans-trenders do not seem to comprehend basic biology, this issue shows that we need to bone up on it ourselves.
Male seahorses do not get pregnant.
The female seahorses lay the eggs.
The male seahorse has a POUCH. Ask any biologist who focuses on mammals why that's an important distinction.
(Hint: Placental mammals vs. marsupials!)
For pregnancy you need two things: the fetus actually inside the parent's (mother's) body, and the fetus actually ATTACHED TO the inside of the parent's (mother's) body and exchanging nutrients and waste.
Take a human female and shove a random strange fetus into her uterus: not only will that hurt a hell of a lot, but it doesn't cause a pregnancy.
So next time you run across a TRA making this stupid argument, remember what you read here.