"A lot of cans now days have a liner in them, I've read that its a resin that is sprayed inside the cans and cured sometime before filling. How do you tell if your can is liner free or not? "

A good point. My understanding is aluminum cans used for cooking should only get as hot as boiling water. Anything hotter will begin to melt and/or burn off the plastic liner. Personally, i wouldn't eat that popcorn. It probably contains burnt, decomposed plastic. Unless anybody here knows of a brand that doesn't have the liner.