It's a malt beverage. Sometimes the bottles say, "flavored beer." YMMV. Technically, by Federal standards, Mike's is a beer since it is a malt beverage and is not distilled.
That said, the port folks on our last cruise didn't even blink at my beverage cans on the XRay. They didn't ask, nor did they look at them. I could have brought anything in a can onboard.