Furnace Pressure Switch Testing
Measuring resistance on an element in a live circuit can produce weird results.

Disconnect one of the wires from the switch (or both if they're molded into a single connector), then measure the switch again while the inducer blower is running. The furnace controls won't detect the draft and will probably throw an error, but that's fine.

Switches can fail to a relatively high resistance state, but I'd guess it's unlikely.