Nah, its not possible to tell(as you might have figured from this wise guy already). However purple is more common indica leaning than pure sativa strains. So most likely its some hybrid or indica.
Good luck with it and watch out for male flowers! If this seed came from weed that was not properly seeded, it is likely that it came from a plant that started to make male flowers and seeded itself. If so, it is likely that this plant will also start to make male flowers at some point, but it might not. If it does, its most likely few here and there, and you might be able to pick them off before they pollinate anything, or they might appear only if you flower it for too long.
If it was seeded by another plant that went hermie, then it has a smaller chance of starting to make male flowers, but still enough to look out for them.
This is the risk with bag seeds. Personally i would never plant a random seed from bud, no matter how good the weed was. But roots of many classic strains are from bag seeds and people do successfully grow them to equally good weed they found them from. But its a risk i would not personally take.