CO2 tanks have gas over liquid. Co2 is a liquid at higher pressures. They make the tank cold by filling and purging, so they can get the full amount in. Look for the tare weight on the bottle, weight it and see if you have close to 5 pounds in (tare+CO2). Keep it at room temp and come back and check, the pressure may go up. If I put a CO2 tank in the keezer to carbonate lagers, the pressure is low on the tank gauge, but no worries.
Also note that the regulator will stay at a high pressure, until the liquid is gone, then it drops rapidly.
If they just equalized pressure, not a correct fill.