This video has a decent theory about the seeds packages:
Basically, says the theory, the seeds are coming from Chinese online sellers as part of a scam, though not one against the recipients of the seeds.
Here's how it works: online marketplaces in China are highly competitive and the high placement of one's store in the listings is dependent in large part on how many orders the store ships, and how many good reviews they receive from customers. The products are cheap garbage so the good reviews have to be faked; but in order to combat fakery, the online marketplaces require shipping confirmation numbers to prove that the person leaving the review is an actual customer.
Enter this scam. The seller obtains names and addresses the same way any spammer does, and mails out these packages to random people outside China. In this way they create "real" shipping labels and info, and once they receive confirmation that the package has been delivered, they log onto the markeplace pretending to be the recipient using their shipping confirmation number and leave a good review for themselves. The products they're pretending to sell aren't seeds; they can be anything - bracelets or sunglasses for instance - but seeds are sent because 1) they're even more worthless than the cheap products they're actually pushing, so they lose nothing and 2) seeds can be measured out to a very precise weight which is necessary because the actual weight of the package has to match the stated weight of the alleged product being mailed in order to get through Customs.
