Hacker1001101001's probable bump spamming should have been apparent to the admins when he was unbanned, and given the amount of time that has elapsed since I believe he did this, I don't think it would be appropriate to prosecute him for this.
FTFY. It was not apparent, therefore your argument is nullified.
We may disagree on the "probable" point, but I don't believe the presence of this word changes my argument.
The bump spamming (probable or not) should be able to be detected by the admins. If someone is using sockpuppets to bump spam a bunch of threads, IP evidence should be obvious. Page viewing history is only available to the admins. If someone is part of a bump spamming group, the admins should be able to detect this. It is not trivial to obtain all the posts that exist in the forum, and once someone obtains all the posts on the forum, performing substantive analysis can be resource-intensive. Being that resources necessary to run the forum are not consistent throughout the day, analysis to detect harmful things can be performed during off-peak times.
If hacker1001101001's misdeeds were not apparent to the admins this time last year when he was unbanned, I cannot help that. They should have been. His misdeeds were highlighted four months ago, and the admins chose to not take action.