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.
Strawberry and banana are 8.5/10 for milk bottle fans, but the chocolate is a 2/10 and drags the bag down to 5/10.
Russ admits he doesn't like milk bottles, calling them a low-tier lolly. The strawberry and banana flavours are 'bang on' at 8.5/10 for fans, but the chocolate one is 'fucked' at 2/10 and tastes like Lynx Dark Temptation body spray. That brings the whole bag to 5/10, which matches the on-screen graphic.