Yes the naming is nonsensical, because the intelligence ranking is this (with atomic numbers in parentheses for those that don't have the periodic table memorized):

Carbon (6) > Hydrogen (1) > Argon (18).

Double nonsense because it appears Hydrogen is in fact a smaller model than Argon, in which case this should obviously be released as "Gemini 4.1 Hydrogen" or something.

What they probably should've done if they really wanted to use elements is to do noble gases, and start these first three models in the middle (to leave room for bigger/smaller models in the future).

So you'd have:

Argon => Argon (18)

Hydrogen => Krypton (36)

Carbon => Xenon (54)

Not exactly because as noted it appears hydrogen is in fact the smaller model, but then this should be (again) 4.1 or something.

And they'd leave space for a truly massive model if needed (Radon) and two slots for much smaller models, with Helium (2) presumably being a model that could be run on basically any consumer device.