Just because the EU gets involved, doesn't mean NATO will follow suit.
There's an argument that EU is the aggressor for the purposes of Article 5 if it comes to the aid of a non-NATO member. The USA and other non-EU members would have the option to sit that one out, if they wanted. Alternatively, they could offer support to only NATO members.
This is probably part of what's spurring NATO membership. I bet most Fins and Swedes thought that the USA would deploy forces the event of a conflict. Now they see that American policy will be aid only, regardless of the death and destruction.
> There's an argument that EU is the aggressor for the purposes of Article 5
There is no such thing as “an aggressor for purpose of Article 5“; and the only case to be made for an “aggressor” status that would obviate Article 5 commitments is an aggressor under international law (that is, someone engaging in aggressive war in violation of the UN Charter, North Atlantic Treaty, and customary international law.)
Participating in individual or mutual self-defense action outside the scope of NATO doesn't void Article 5 (we know, because it didn't, despite definitely being part of the scenario, in the only actual Article 5 invocation in history.)
Mutual defensive pacts are not transitive. Germany being in NATO does not mean that every country Germany has a defense pact with is de facto in NATO.
Finland probably doesn't want to find out the hard way how the USA is going to decide to roll here. Being a NATO member removes all doubt as to what happens.
There's an argument that EU is the aggressor for the purposes of Article 5 if it comes to the aid of a non-NATO member. The USA and other non-EU members would have the option to sit that one out, if they wanted. Alternatively, they could offer support to only NATO members.
This is probably part of what's spurring NATO membership. I bet most Fins and Swedes thought that the USA would deploy forces the event of a conflict. Now they see that American policy will be aid only, regardless of the death and destruction.