When it says conure on the packet it probably generalises, i.e. means a sun conure sized bird (a sun is probably an average/mid sized conure and a very common pet). This is a guess though.
As for eating, there's 2 things you can do while observing his food bowl and not taking him to the vet (but take him if he starts behaving lethargic or takes a noticable weight change):
1. Weigh him now. Then weigh him this time-ish for the next few days to see if there's any change. If your scales are bad like mine then a gram either way isn't bad but a consistent change is.
2. Check his keel bone and weight distribution. You want your bird to lie back for you (you may have to hold him carefully if he wiggles) then feel gently the front of his chest, the bone in the middle is called the keel bone, you want to gently feel the shape of the body around that. In the link below is a chart stating the shapes you want to feel for.
http://www.pfma.org.uk/_assets/docs/pet-size-o-meter/pet-size-o-meter-birds.pdf
Be gentle with your bird, maybe wait for him to be settled when you do this so he doesn't get over stressed as this may be a new thing for him.
Edit: Not all birds are the ideal weight, this is because they are bigger or smaller than the species profiles so don't worry too much if your birds isn't exactly 72 grams.
Also keep an eye on your birds behaviour, lethargy, sleeping more than normal, lowering of energy, and generally not being himself.
Edit 2: Personal opinion alert, I think Green Cheeks are on the slimmer side of the the bird scale, like between size 3 and 2 on the chart I linked (leaning 3 probably). So don't fret as well if your little bird is not a perfect 3. Personal Opinion over.