Answers bump questions, and deleting the answers doesn't unbump them. This is pretty much by design. Summarizing the linked post, the idea is that if deleting the answer unbumped the post, it'd provide a way for people to post bad answers without any of us noticing. They could post a spammy/offensive answer, delete it (unbumping it), then wait til it's off the front page before undeleting. If you try to fix this by making undeletes bump, then people can undelete their own answers to bump questions.
That said, when I saw that meta.SO post, I did comment on it expressing my displeasure - this is still pretty annoying, especially to <10k users (who are by far the majority). I wonder if perhaps mod deletion could unbump questions, while leaving self-deletion alone.
With respect to your second question, if a person is actually gaming the system by creating new accounts, the system (or the moderators) will catch on eventually - we have tools for that. I think in this case it's just a coincidence, though. Their writing style wasn't the same.