It's an overreaction if he didn't first ask them to leave if they aren't gonna buy. If they refused to leave, then calling the cops is within bounds. But, yeah, the manager probably over-reacted, but still the guys should be smart enough to know that it isn't a bus stop or a homeless shelter.
If they slip and fall in there, they could sue. The establishment takes those risks (and hires people to clean the nasty toilet) because they want to make profit.
Those dudes should have consideration of that, rather than be arrogant. And the manager should probably have approached it with "people skills" rather than call in the guns so quickly.
I've heard that (in response to this incident) starbucks now lets people use the toilet without needing to make a purchase. I hope it helps their bottom line, but I feel bad for the people who have to clean those toilets.

