Being seedy just means that at some point it got pollinated. Depending on wether the gardener was careless (with either nutes, length of flowering, not removing hermies, leaving a male in the flower room, curing...) or if they needed seeds and sold the 'extra' bud, you may end up growing better bud than you purchased. Also some growers only sell the 'secondary' buds, saving the good stuff for themselves.

I started out learning from bagseed many years ago (before seed banks on the internet) and often grew cannabis that was better than the bagseed. Pretty good feat, considdering the only "good" lights, were mercury vapor.

In the long run tho, (after you've practiced with bagseed) It's best to get good genetics so you know that questionable results are not from questionable genetics.