Ok, so without being there, I can wager a guess how this went down.
I'm wiling to bet a pretty decent amount of money that this was a precurser stop. Meaning, they probably already had surveilance on this guy and they waited till he did any traffic violation and executed the search.
It says "unclear why they think he possessed drugs". They most likely already had this guy as a dealer/user. I know the headlines sound crazy "blinker leads to cavity search", but I bet they aren't telling the whole story. This is a routine thing (not the cavity search). You build intel on the guy, then you wait for him to conduct a traffic infraction and then you stop them. This is all to set up a clear chain of seizure/stop. It's so that if they did find alot of drugs, it won't get thrown out based on unreasonable stop. This is actually a good thing, because it adds an extra layer of legal protection for us.