Dunno. I mean, it's all speculation, and I see how it could be many other actors. But imagine someone blowing up a German wind farm, and the German government saying, "hmm". Russia is generally quick to anger.
Also the political risk for everyone else seems suicidally high.
On day 1 nobody except the culprits knew wtf was going on.
I wouldnt read too much into their hesitancy to comment.