Thirsty Aardvark 30 oz Tumbler, Double Wall Vacuum Insulated, Stainless Steel Cup with Lid (Silver)

This tumbler does the job, ice stays cold forever, and the lid works great. No complaints from me. I like it.

I've had this cup for a little more than a year and it has rust spots inside the cup, can't really be stainless steal, can it?