Let's look at this from the pilot perspective and the FA perspective:

Pilot perspective:
We don't know what the FA told the pilot, but let's suppose she told the pilot that a passenger was intoxicated and confrontational. The pilot has no choice at this point but to eject the passenger. I suppose he could tell his co-worker (the flight attendant) that he does not trust her judgement despite the fact that is it her responsiblity to gauge whether passengers are intoxicated. He could then set a process in motion that would delay the entire flight and lead to one or the other of them to be reprimanded for bad judgement. If it were me, I'd trust my co-worker and contact the gate agent to begin the ejection process and get back to my pre-departure checks (you know, the part of my job where I am responsible for making sure the plane is safe to fly, etc.)

FA perspective:
Drunk passenger confronts you during the boarding process. He does not threaten other passengers, but now that he has confronted you in front of witnesses, you are obligated to eject him.

From the companies perspective, it might be good to have a redcoat explain the situation to you. Did this happen?