That looks like a liner. I think all food grade drums have liners so they don't react with the metal. Mine was a food grade barrel and I had to burn out the liner. Check out the first few pages of my UDS thread. Rocky at BDS used to use drums with liners but switched because it was such a PITA to burn them out.
I don't know if having the liner in there is unsafe or not. I would definitely be checking for off/chemical smells during your burn out.
Wannabe BBQ Illuminati