I didn't set it up beyond creating a skeleton "Event", cause I have zero interest in paying real money to kick the tires on this, but as I understand it one would add existing repos to their AWS Code* tooling, at which point machine learning awesomeness takes place and it surfaces findings (inside those AWS CodeWhatever APIs, having nothing to do with BugBust)
If those findings are imported into a BugBust Event [which is defined by the tuple of (start date, end date, scoring, and repos in scope)], then one can (invite|publish) a link to the BugBust Event and at the end date the participant who fixed the in-scope issues with the highest point values claims the cited prizes. Further (again, AIUI), at the end of the *AWS* event, the BugBust account who has the most *overall* points wins a re:Invent trip
I don't believe AWS gets into the business of monitoring the PRs, only observing the CodeWhatever outcomes -- if CodeWhatever found an issue, time elapses, and the CodeWhatever sees the issue is fixed, then BugBust will look up the category of said issue, multiply it by the assigned score in any Events it is associated to, and award the Internet points to any Event participant it knows about