^^Popcorn nugs aren't always bad. The only time I've found real mowie wowie or chocolate thai it was popcorn nugs. Both were pure sativas that kicked my ass.
Many chronic strains have hermaphroditic tendancies in the genetics from plants being forced to hermaphrodite to produce feminized seed stock. Especially with Northern Lights I often find 2 or 3 seeds per quarter.
In my experience, a bud with a few seeds in it is actually more potent than sensimilla bud from the same plant. I can understand being a bit pissed about finding seeds in a gram sack, though.
If there are a few seeds, they were probably caused by hermaphrodited flowers on the plant. These seeds are feminized because a hermaphrodite flower can only give its X chromosome. Males are extremely rare from these seeds, and usually the result of environment rather than genetics. If there are a lot of seeds they are probably from a mairried plant, which produces both male and female seeds.
If the bud is good, don't stress. Just enjoy it. Hell, if the bud is good plant one of them seeds somewhere. I like the idea of planting them in the park. Even if you never go back to that plant it might survive and make bud or seeds. Make the weed "problem" in your city as "bad" as you can. :D :D :D