No, terrorism act being ruled out means police doesn't have evidence or even suspect a terrorism motive. There is no separate "terrorism" singular statute for violent crimes. Rather Finland handles this by having qualifier for list of crimes of "crime act done in terroristic intent". One of these is explosives crimes. Illegal possession and so on. Then going to stuff like "murder with terroristic intent" and so on. Only real pure terrorism crimes are stuff like "leading a terrorist group", "training for terroristic group" and so on organizational crimes.

What specifying in article means is police has told they have no indication of terroristic purpose/motive and thus the investigation will start regarding just "plain" explosives crimes, instead of starting investigation on "explosives crimes with terroristic intent". Basically initial show doesn't show anything related to terrorism. The amount of explosives is itself irrelevant. Since the whole thing about the Finnish terrorism statute is about the motive and purpose, not the means.

You could blow some single person with a whole metric ton of explosives and not be charged with terrorism. If you did it for say as crime of passion since they were having an affair with your spouse, that isn't a terroristic murder with explosives. It's just plain murder for personal reasons, just way over the top amount of explosives. You probably would get charged with public endangerment againt since that is awful big explosion and so on. However again.... you didn't endanger public for terroristic purposes so no terroristic crime label. You did it rather out of not caring/stupidity and so on.

Also I would point out as result of couple big European wars and having a pretty sizeable mining industry, even large amount of explosives might be accessible to certain people. Which is why on the other hand authorities really take dim view on explosives crimes. He might not be suspected of terrorism, but I would think the person will get book thrown at them (as much as anyone gets book thrown at them in Finland) to make example. Prosecutor will must likely seek maximum jail sentence for that kind of pile of illegal explosives (whatever they were before, they certainly are illegal upon being put upon some randos car boot, which is not a legal way to store 12 kg of dynamite). Probably aggravated explosives crime at that again given it's 12 kg of dynamite. You can make awful big crater with that amount.

Also I would at while police is at the moment ruling out terrorism, it isn't a court judgement. They are allowed to change their mind, should they find evidence making them suspect terroristic purpose. It has happened before. For example the last right wing terrorism case actually started like that. They found a stash of firearms and explosives. However first those were being suspected to be tied to drugs crimes and were found related to a drug bust investigation. So the investigation didn't start as terroristic. However after couple home searches related to that investigation were done, police found evidence suggesting terroristic purpose. This lead to the crimes classification changing to firearms crimes and explosives crimes to firearms crimes with terroristic intent and explosives crimes with terroristic intent. Plus on top as I remember preparing a terroristic act and so on. They were caught before they actually carried out an strike with their stash.