He calls Ilima, a male, a "dreamboat". There is also something in his anime in his debut episode but I forget what it is. It's probably nothing, but I've just been thinking about Rotom Dex a lot.
The Rotom-Dex is genderless, as Rotom itself is genderless and is connected to a machine, and machines like the pokedex do not have a gender.
P.S: I do not want to argue about this, I'm just stating facts, so please refrain from commenting how you're triggered by me stating fact.