Old timey "flotation" tires run 22-35 pressure range. They're awsome easy on soft or loose surfaces, but they are truly a drag on smooth pavement. Thickwall moped tires often run low pressure also, but they weigh a ton, as well! Could this be what you have? I would expect most decent modern BICYCLE tires in that size to claim 45 lbs, or a range of 30-65 lbs, adjust to suit terrain and rider.
I thought about mentioning your gauge, the little hand held blow out kind are usually close, or they don't work at all. Dial gauges can be more precise, but can also be way off.