Believe it or not, massive governments that employ hundreds of thousands of people are capable of doing multiple things simultaneously.
I don't think there's any evidence this was state-sponsored, or even state-approved, but "oh there's better things to do" is not a good argument in the least.
I'll keep it in mind the next time a horse bolts from a barn in some foreign country - 'Clearly, this was the CIA's doing. There's no evidence for it, but they have the capability, and their motives are sufficiently sinister and shadowy, and while there's no reason for them to be engaging in medium-scale hooliganism on the other side of the world, they could be the ones responsible!'
The Russian Government had huge motive for this attack, they were not at all happy about the United States' retaliation for SolarWinds/Election interference. Shutting down a major oil pipeline in the United States is not "medium-scale hooliganism."
Also shouting 'No Evidence' is a typical tactic the propagandists use to cast doubt and muddy the waters; surely the attackers would love to see what evidence is available, so they can adapt - that's why evidence is largely kept private.
Why do you assume that propagandists only work for them?
What makes you think propagandists on our side would never use lack of evidence to make whatever they want up, and cite your exact reason as justification?
This is medium-scale hooliganism in the sense that the end result isn't going to accomplish more than a dedicated idiot with a toolbox, and a grudge against gas pipelines couldn't achieve. IT will clean things up, operations will resume, life will go on.
Not to mention that this gives the industry another, rather low-stakes kick in the ass to take IT security seriously.
I don't think there's any evidence this was state-sponsored, or even state-approved, but "oh there's better things to do" is not a good argument in the least.