Definitely not a lab diamond. A lab diamond is 100% carbon.
Whatever it is it’s probably closest to Moissanite.
Not sure what their point is with “GIA grading standards” as GIA doesn’t grade Moissanite or any other stimulants.
Also not sure what’s having carbon in the formula is supposed to mean (if it actually does) a lump of black coal is 100% carbon but not something I’d wear as a gemstone!