Ostensibly, it was to prove Wiebe wasn't using a legit PCB in his cabinet. There are claims that the film took dramatic license and that they actually had permission to investigate the machine, but those come from Billy and his friends, so...yeah.
The King of Kong movie is pretty worth watching, regardless of whether you care about the record itself, but it does have a pretty obvious slant.
@Jean Lafitte 1812 posted
this Summoning Salt video about the record that goes into the record disputes a bit more, and he also talks about the specific runs that were the subject of the dispute that led to Billy's scores being removed from TG. Salt did the video a few years ago, however, so he only casually mentions the oddities surrounding the runs. But it does also kinda demonstrate that TG was historically very...favorable toward Billy during Walter Day's time, which is a pretty sharp contrast from how it treated him under Jace Hall.