The cooking sprays that come in a can (all of them that I am familar with) are not pure oil - they are a blend of oils and include added lecithin - which gives the spray it's non-stick quality ... BUT can cause the pan to develop a sticky residue if too much is used and ESPECIALLY if sprayed on non-stick cookware. The problem is that the lecithin is a chemical cousin of non-stick coatings - it forms a chemical bond which causes it to form an incomplete polymer (like not properly seasoning cast iron to fully polymerize the oil - leaving a sticky residue) - it has nothing to do with the propellant used as far as I know.
Now, I will admit that I have not read the labels of every iteration of every brand of cooking spray on the market. But the ones I have read seem to all agree on the "do not use on non-stick cookware" idea.
I can't use canned non-stick sprays indoors because I have asthma - it has nothing to do with the propellant - it has to do with the amount of fine particulate matter (mist) in the air. I have no problems if I go outdoors to spray it as long as the wind is at my back. I have a similar problem using a spritzer bottle to spray pure oil - just not as much of a problem because the mist is not as fine and does not linger in the air as long.
Personally - I find that if I pour a little oil into my pot/pan and wipe it around with a folded up paper towel I achieve the same results - I wind up with a small amount of oil coating the surface without it being aerosolized - and thus no over-spray that I have to wipe up off of the stovetop or a counter top.
Now - back to momerlyn's post ... I had never seen that either, but in some ways it might make sense. The heat will break down the surface tension in the small spray particles - allowing them to spread out and provide a better more uniform coverage of the pan surface.