He said every 2-3 weeks. If it’s all 4 wheels it’s likely temperature related.What everyone said - inflation pressures will vary 1-3psi based on temperature swings.
However, in my experience, if one tire (or more) regularly loses that every few days it's because of something leaking somewhere (hard-to-see nail etc, cut in tread - glass damage, leaking tire valve stem, etc.) Worst case (you are in NYC) is pothole damage to wheel or tire - hard to see on the inside area of wheel/tire). Another situation I faced was with a tire gauge that had grown "tired" (old) and was often inaccurate - I replaced that one.
For starters get out your spray bottle of soapy water and start investigating.