Yeah that's almost certainly not an occupancy sensor. Out here the single space meters have green LEDs for when it's legal to park (e.g. non-metered hours, or metered hours and the meter has been paid) and red for when the it's not legal to park there. This is so that someone passing by can quickly identify which meters to focus on.

Of all the ways you could detect the presence of a car most would be easily obstructed if they're looking from the POV of the meter. Maybe a camera would work, but even if you ignore the ease with which it's obstructed you still run into issues processing the photos. Sure you could also probably fit a small SBC into there, but you'd have no room for a battery powerful enough to run for any meaningful amount of time.

When I was doing that sort of thing professionally we kept the stuff in the meter very simple and our whole thing was built on super low power comms (think lower power consumption than Zigbee). While batteries are easy enough to change out in a meter, having to change them out frequently adds to the operational cost. The costs of trying to determine occupancy outweigh the benefits.

Typically what I've seen is that adding money to the meter just resets the session. Dollars to donuts you just came across a busted meter.