It says "female body" on Pixiv rather than "female clothing" which is what they use for cross-dressing. Apart from the fact that she seems to have cum dripping from her pussy, has tits and has no balls. IIRC none of the guys wear fake tits in that scene.
I know what you mean. It doesn't help that cross-dressing Yosuke is usually drawn really femininely rather than how he looks in the game - like a guy in a dress.
It is amazing how much Yosuke x Souji art there is. Click on the P4 tag on pixiv and it's absolutely everywhere. The second most popular couple, from my observations, Souji x Naoto, has a lot, but not nearly as much. I wonder why this is the case here.
And yes, the confusion of "is this a genderswap or crossdressing?" sets in a lot.