Sure it is, you just need imagination. Say that you are a stalker, you (or someone delegated by you) passed near your target and got h(daykey, time), your target happens to go to the hospital for covid a while after, so you have the daykey of your target for multiple days and all of their h(day, time). You detect that it was your target that went into the hospital because one of their h(daykey, time) matches with the one that you have stored, in addition you know if your target passed nearby you/one of your friends/one of the locations where you have put some cheap bluetooth phones and the exact day and time that this happened. Intentionally infecting the target will covid will help this whole thing but it is not necessary.