Obviously theres the leaf sizes. thick for indica, thin for sativa. but what about hte ones that are kinda the sameish. Is it the amount of time it takes trichs and hair color to develope? can it be found out that way? Example: You have a nug with a little bit of redness showing on the lower parts of the bud and the trichs are still crystal clear. the hair is then fully red in a whil and the trichs .... where am i going with this. idk.
strechy plants are generally sativa dominant. indicas generally dont stretch so much satival leafs are long and skinny while indical leafs get quite broad.
Not too many strains are 100% one or the other, so most likely you are looking at a hybrid cross of some kind.