The proposal to fake sex came although on the "more than friends" path, but it came from Josy independently of the MC. So it's clear that Josy has this idea in her head on "friends" path as well.
Depending on player choices you can have sex with Josy and Maya before the decision, but you can also choose to avoid most sexual actions with them except for some kissing.
The game would have to discriminate all those different paths :
- DIK, neutral or CHIK affinity
- friends or more than friends
- had sex with Josy or not
- had sex with Maya or not
The suggestion to just fake the sex tasks would cover all these different combinations (least common denominator) and would probably be "cheap" to implement , allthough it feels strange if you had sex with them before.
(So the "faking" might be a Game Design decision rather than a character decision.)