It's not like he doesn't eat! He just has to get ready-made food from the grocery store, multivitamins, and other people to cook for him which isn't great but he's not dying at least. Sometimes he misses Aoba, who would always cook for him before he disappeared from this world. Tsumugi is probably completely unaware that Midorima actually enjoyed his company beyond sharing lucky items and space, but that is the way that being in Midorima's life can be sometimes.

"I have no need to wear a bib. I simply meant that I eat much more, you fool. All Cordis-blessed have a strong appetite for food and chroma and a metabolism that makes it necessary."

Saying it factually makes it okay. Takao will discover that fact whether he wants to or not, whether it's with Midorima or not. And he's going to be hanging around Midorima means that he needs to find out in a way that's safe, and that's what exposition is for.

If he gets a bib, he may try to suffocate Takao with it, but that's for a later date. (Unless it's a lucky item, anyway.)

With his home nearby, they're already at the front door again. Merlin is in the window, watching sadly where he was abandoned for basketball.