Hi Invo,
Indeed, in certain contexts, the word “kāya” has other meanings. However, in this particular context, “kāya” means “physical body”, as explained in the Commentary (Mp III 232):
imameva kāyanti imaṃ karajakāyaṃ. abhisandetīti temeti sneheti, sabbattha pavattapītisukhaṃ karoti. parisandetīti samantato sandeti. paripūretīti vāyunā bhastaṃ viya pūreti. parippharatīti samantato phusati.
“This body:” this body born of action (i.e. born of kamma). “He drenches:” he moistens, he extends rapture and happiness everywhere. “Steeps:” makes flow all over. “Fills:” like filling a bellows with air. “Pervades:” reaches everything [in the body].
sabbāvato kāyassāti assa bhikkhuno sabbakoṭṭhāsavato kāyassa kiñci upādinnakasantatipavattiṭṭhāne chavimaṃsalohitānugataṃ aṇumattampi ṭhānaṃ paṭhamajjhānasukhena aphuṭaṃ nāma na hoti.
“His whole body:” in this monk’s body, with all its parts, in the place where produced [material] continuity occurs there is not even the smallest part consisting of skin, flesh, and blood that is not pervaded with the happiness of the first jhāna.
So, despite the shift to the “mental body” in the later literature, the Commentary still preserves the literal “physical body” meaning in this particular context. And explanation in the earlier sources, namely the Paṭisambhidāmagga and the Vimuttimagga, gives support for such a reading.