They flipped your "jet-can" while you mine and then you try to take the contents back;
How does this one work? Wouldn't the "flipping" mean they get tagged for pvp first?
yes, however dont try to steal back from them as it will also flag YOU to THEM allowing them the oportunity to make the first strike.
The high sec griefers do this to bait the newer players who dont know the way flagging works. Let them steal , put a tell in local so other miners are aware and move on, you will have lost some ore but in the long run this is cheaper, as usually they will have stealthed mates nearby waiting for your "aggressive" move.