Their sizes were hardly different, as the chakra punches kaguya was firing at naruto were larger than her own body just like the ones she fired at sasuke's PS.
They aren't air pressure since we explicitly see kaguya manifesting a chakra aura around her which the chakra punches spawn from, and gentle fist's air pressure does not take the form of a fist, nor does the fist have rikudou chakra markings on them.
And sure, we can't say FOR SURE they are the same thing, just like we can't say FOR SURE that Sasuke's PS for some inexplicable reason got massively less durable in the last chapter than it really is. However, the evidence is compelling that Kaguya used chakra arm punches against both Naruto and Sasuke.