The moisture was probably the compressed liquid in the can. If you invert the can and spray it can be used as freezer.
Some cans are designed to be used at any angle and others not.
The "liquid" used to be HFC134 (the stuff used in aircon systems and freezers etc) one reason why the stuff has gone sky high in price... it's damaging to the environment. Don't know if it still is.
Trouble with compressed air is it blow the dirt everywhere. I much prefer a small brush and vacuum for anything like that.