Every number is Russ’s own rating out of 10. Russ has previously stated that he never scores in sponsored videos, so the food he reviews carries no applied pressure or bias.
Russ remembered an older 'great bubblegum' version, and this looks like normal bubblegum. He says it tastes like Hubba Bubba Outrageous Original with little aftertaste and rates it 9/10. An earlier 'Really not great' line contradicts the final verdict and may be a mistranscription.