It's not strange at all: Canada extradites people if the actions they are accused of are crimes in Canada.
Drug trafficking, for all that it generally isn't enforced in the case of marijuana, is illegal in Canada; so a Canadian accused of trafficking drugs into the US was extradited. Selling prescription medications to patients with proper prescriptions is legal in Canada.
It appears that, while non-viable seeds are explicitly legal, there does not appear to be any prohibition against viable seeds, unless they are considered a marijuana "preparation". I suspect there's some case law floating around where a court has decided whether or not cannabis seeds are considered a marijuana preparation.
Edit: Erowid is somewhat helpful in this regard, although the linked article is broken:
I am not a lawyer, but I would be very surprised if Canadian courts didn't interpret that text in accordance with the general principle that all words have meaning -- i.e., explicitly stating that non-viable seeds are legal implies that the intention was that viable seeds are not legal.
I was under the impression that the law prohibited viable seeds but due to a loophole (you can't be certain a seed is viable or not) they couldn't stop people with any seed. I might be remembering this all wrong.
Drug trafficking, for all that it generally isn't enforced in the case of marijuana, is illegal in Canada; so a Canadian accused of trafficking drugs into the US was extradited. Selling prescription medications to patients with proper prescriptions is legal in Canada.