I think it is dodgy to have an online election, and then disqualify participants for mentioning it to people who might want to vote for them.
Regardless, the tweets in question were around a long time before Pinboard was disqualified without expectation. The first one certainly predates kevin's phone call, for instance.
(And of course one of the tweets in question was contained a link to the general poll, which was not a submission of Maciej's, and the other, technically, was a link to all the Apply HN posts, not to his.)
Certainly it never crossed my mind that the rules about voting rings would be any different than with regular posts. HN users are passionately opposed to the voting system getting gamed; we'd have been skinned alive if we allowed it. But tptacek makes a good point about that not being obvious to everybody.
Your rules about voting rings are not public. I think that you're so used to modding the site that you forget this, but take a look at the letter of what it actually says in the FAQ.
I told him when I noticed the same Twitter post that it was going to cause problems (too late!), and he was genuinely surprised.
But that says nothing about the Apply HN situation. That's new, had a different set of rules (hell, you wrote a polling solution), and the regular guidelines didn't necessarily apply. That they did should have been made clear.
Again, nothing against it this time, since it's all up to you guys - just feedback for the next time.