I think that is the most likely scenario. Lehterä might not even know what has happened, but if he has given keys to his cottage to some old friend of his who has done something with cocaine there, police will include Lehterä in their investigation. And there wont be any consequences for Lehterä if that is the case
Some of those arrested are suspected distributors without a doubt to warrant for arrests and the whole works, but it's not against a law to merely associate with a person who happens to be a distributor. Obviously if your buddy loaning your cabin for a weekend has a big enough stash with himself the question if it all is for personal private use or for selling purpose will arise from that.
It will turn bad for Jori though if his own actions around the matter start ticking the boxes of any crime described in the Crime Act.
Finnish Crime Act defines a "narcotics use crime" as, among other things, being in possession of a small/negligible amount of drug for personal use. If you're in possession of more than a small amount, it legal-technically becomes a "narcotics crime", under the title of which is everything like manufacturing, importing, selling and possession, so the intention to distribute or lack of doesn't really matter as the label of the crime goes. Punishable by fine or up to two years in prison.
If there's a plenty of drugs and intent for notable economic benefit or it's particularly organized, it becomes an "aggravated narcotics crime" which is more serious business.
The seven persons still arrested are in for aggravated narcotics crime, money laundering and professional hiding of stolen (etc.) property. They report "apprehensions" have been made at the Lehtera cabin, but we don't know if those have merely been some fringe persons. Lehtera has been interrogated (and denies), so technically he can be one of those apprehended (for the interrogation) from the cabin. In Finland the police only
apprehends you; the court will decide in the following couple of days if you actually become
arrested. They think they got something on you if they go so far.