I've never heard of this either. Why would anyone want to sniff propane? It has a nasty odor, like rotten eggs.
Propane, like natural gas, has a touch of methane or some other smelly gas added to it so you can detect leaks. Otherwise you would never smell a leak.
What does natural gas smell like?
Rotten eggs: a bad smell for a good reason
Natural gas and piped propane smell like rotten eggs or sulphur. Because natural gas is odourless, we add trace amounts of a chemical called mercaptan, which has a distinctive rotten egg or sulphur-like odour. It smells bad for a good reason! In case of a leak, we want you to be able to detect and identify it. We never charge to investigate gas odour calls.