@yvanzo The guideline for multiple titles does apply to track titles “When a release is a re-release of two or more other releases, a track includes two or more songs, or a…” (emphasis added).
Seems like, though, if it’s printed on the release as part of the title, it should be part of the title here. And I’m guessing that “medley” there means an arrangement of the two songs, not just them being played one after the other. If so, that’s strikes me as not two titles for two two works on the track. Instead, that’s one title for one work (based on two others) named “Medley: Aquarius / Let The Sunshine In”.
Even if you did take it as two titles, presumably you’d add “(medley)” at the end as extra title information.
@ardain BTW: it’d help to link to the relevant release (just copy & paste the URL if nothing else) especially if the cover art is uploaded there.