Odd experience: USB flash drive larger than stated after formatting it

I do take testing computer devices like with with a grain of salt. I have a laptop that is absolutely horrible and use it only to test Vine computer devices.

The USB flash drive was advertised at 128 gig. That's what it showed up when attaching it to the computer. I ran various virus and other tests on it and it appeared clean.

To my surprise, when I reformatted it this morning, it's showing up at 512 gig. I don't know whether to be pleased or suspicious.