Of course, it's an assumption that they didn't first go to the leadership.
Yes it is .. but having been a member of a church for 20 years, I can tell you those who whine the most in public are most usually those who won't visit the pastor privately, because he might tell them their wrong .. so they go public.
The Bible calls such people "factious" - or somebody who just stirs the pot. If they're so unhappy with the Pastor's actions, then it's just better that they leave.
It's sad, but it's more common than most people know. People believe they are obligated to tell the Pastor what to do .. they're not. If more people would study how a church is supposed to function, they wouldn't get in all this trouble.