Looks like, from my perspective, Yukari and Fuuka sold Shinji some photos of FeMC with her hair down in exchange for some extra grub.

A good deal on both ends, I must say.

seems about right. Shinji's first panel with him snapping shut his cellphone seems pretty clear to me.

Fuuka be making the menu for the next meal?

This is surprisingly in character, its not like they were taking dirty pics of Mshe either after all.