In an empty room

A CO2 level of 1768ppm shows that the ventilation in this room is completely inadequate. If there had been someone with covid in the room fifteen minutes before then there could still be covid virus floating in the air and someone entering this empty room could get infected.

Now consider the cubicles in a public toilet. SARS-COV-2 is excreted in the stool and flushing the toilet is known to create a plume of "faecal aerosols", especially if the lid is not down during the flush. (And how many public toilets have lids on them?)

The ventilation in many public toilets is poor anyway and obviously the ventilation in the enclosed area of a toilet cubicle can be very poor. Person A, with asymptomatic covid, uses the toilet and flushes. A plume of faecal aerosols is created which lingers in the cubicle. Ten minutes later, Person B, you perhaps, enters the cubicle, sits down for five minutes, inhales the plume of covid-containing faecal aerosols and five days later develops symptoms of covid.

Empty rooms cannot be presumed to be safe.