I agree Sandra, any seeds/plants arriving unsolicited into a country pose a threat to the agriculture. Our area here in Norfolk is very much an agricultural one, growing all sorts of crops, mainly grains, sugar beet, maize and potatoes. If these weird seeds were contaminated in any way and some daft person tried to sow and grow them, a virulent plant disease could be spread throughout the county (and the country), a bit like Covid19 in humans. Or it could kill bees and other insects.
I've watched an interesting TV programme about Australian airport customs control, and they're fiercely strict about anyone trying to bring in food, plants etc. Quite rightly.
I did wonder if it was a wicked plot to scupper plant cultivation, but the 'brushing' sounds plausible too.
Anything arriving through the Post nowadays is dodgy it seems.
I received today a new Bus Pass (it was due for renewal) and in the photo on the card I look like a terrifying witch. Husband fell over laughing, and said what a good likeness it is. Pig.