This is a steel coffee mug.
Some years ago I bought a Triumph-brand "stainless steel" coffee mug similar to that one you received from RE. One day while I was drinking my instant coffee, the handle just detached from the mug and dropped hot "coffee" into my lap.
I really wanted to join the McDonald's lawsuit to pay for washing my pants but I couldn't find enough owners of the Triumph coffee mug to join me in a class-action court action.