My non-alcoholic McGuigan Shiraz is fizzy! Is it carbonation or refermentation?

I’m off alcohol at the moment (I do miss my proper wine!) and opened this bottle of McGuigan Zero Shiraz. It hissed on opening and has bubbles which are still rising to the surface of my glass after half an hour.

I assume it’s not meant to be fizzy. I don’t know what it’s meant to taste like normally but it doesn’t taste ‘off’.

Is it just excess carbonation or has it re fermented? I assume if it’s re fermented then it’s no longer non-alcoholic? How can you even tell?!

Thanks in advance for any info 🙂