I get that nuking the thread absent any solid proof might still be seen as drastic, so how about temporarily locking it for, say, 7 days, or until the OP cleans up all the spammy posts?
Even if he deletes all the spam from bump bots, the goal is still accomplished: the thread stays on top thanks to the spam.
A follow up after reading this:
We ask our community to leave a comment and their opinion about ROOMDAO.
We ask our community to say something about us
That's incentivizing posting, and against the rules. The thread should be nuked. Let me just report it and see what happens.