Perhaps it was that she'd been so kind to him when his father had neglected him for 18 years of his life, and managed to devastate and ridicule Kyle the singular time he interacted with him during that period?

I mean fucking goddamn, Sigma.

In any case, Kyle was aware of biology. He was aware that even if the other didn't want to eat, he needed to eat to live - and that was why Sigma might find that bruised fruit settled on the restaurant's counter beside him, Kyle holding his helmet in one hand as he moved to open the box. Ooh, aged cereal that was still airtight, for now. Wonderful!