The vegetable seed packets were sealed, actually, double-sealed at the factory in Holland.
Yes, but it's still a potential invasive species.
The agricultural aspect of customs is to prevent invasive critters and plants from entering a country. It's not just the plants, but also the fungii, diseases, parasites, and blights that they carry, even in seed form. Sealing live seeds doesn't prevent any of this.
Having worked customs from a military perspective, ANY living plants or seeds are fair game.