I wouldn't rule out a mass panic-type event. A similar event which closed London's Gatwick airport (one of Europe's busiest) garnered no evidence and no serious lines of enquiry.
Don't get me wrong - at Gatwick there were many reports of people seeing drones with lights. The only problem is they weren't - they were seeing something else and reporting as seeing drones because they must have seen a drone - what else could it be?
But, as I said, it looks like the early (earliest?) observations were actually of a school plane. Probably some concerned citizen filmed it, and the authorities didn't immediately realize what it was since figuring out the exact place of a light in the sky in a cell phone video isn't that easy.
Could it still be the Russians? Yes, I guess. But if the first observation turns out to have NOT been the Russians, to me that's a bit like how the first crop circles turned out to be a confirmed prank - yeah, technically later ones could still be aliens but given how it started doesn't that seem implausible?
Not to make a comparison otherwise, of course believing in nefarious Russians is a lot more reasonable than believing in mischievous aliens. But I'm trying to make an argument about a causal explanations and a kind of data-generating process, ... not doing too great a job at it I guess.
I think mass hysteria is too perjorative. We have a lot of suspicious data points, but then a new data point turns up (early lights were a false alert) which suggests that the data generating process may be pretty biased.
Definitively not coincidence, but there are a lot of things that could cause a pattern of reported air lights - such as a warning to be on high alert looking for them, the autumnal equinox (nights are getting much darker very quickly in Denmark right now), etc.
Beyond the fine, the airlines will try to get their losses in millions back from someone. If it turns out to have been a private person, there will be lawsuits. In general parents are liable for their children. When a child is old enough to fly a drone on its own, I think it will also be of partial-legal age. Acceptance of manslaughter and threat to national security is not taken lightly.
The arrest in Oslo were a married couple from Signapore in their 60s. The man was fined and 8000 NOK for admitting to flying the drone and might get deported. They were flying in central Oslo, and it seems unrelated to the drones in Denmark.
There were also unconfirmed sightings of drones around the airport in Oslo. The director of police states that "It is still unclear what was observed. There are conflicting interpretations of the observations that were made".
At least one of the videos published recently was likely of a school plane from Copenhagen Airtaxi, according to a Norwegian drone trade magazine: https://www.dronemag.no/dansk-droneobservasjon-kan-ha-vaert-...