2 Accounts created only for safe third one - against the rules?

Question about the rules:

Two players created accounts solely to block an entire solar system and secure a moon for a third player. Around 90% of their total points come from Astrophysics research. Once they reached the Astrophysics level required to colonize seven planets, they simultaneously colonized every available planet in the system and immediately activated Vacation Mode.

Assuming it cannot be proven that these accounts are multis, could this still be considered a violation of the rules under the provision covering other forms of behavior that go against the spirit of fair play?

I'm not asking whether this is definitely punishable in this specific case. I'm asking whether the rules provide a basis for treating this type of conduct as rule-breaking, even if it does not fall under the Multi Account rule.

It doesn't really matter. We talked to him; he shouted and made some threats for a bit, but in the end, he did some self-reflection.

BTW

Thanks for the reply. I didn't know everyone played that way—I never created accounts to block solar systems. I asked around in the alliance, and they hadn't done it either. But then again, maybe everyone—except us and the rest of the universe—actually does play that way.