I think -
* He's a specialist in this field; why would you doubt his credentials?
* He felt it, looked at it and knew it was nothing to be concerned about; it didn't need any further long look, or questions answering, or any futher discussion. He didn't need to spend any longer- hes a specialist. He sees things day in and day out, its just JOB and what he has trained for his whole professional life. He knows what is a problem and what isn't.
* He found it funny that you had attended for such a minor reason, and commented that he had acute patients with non-benign problems.
* He informed you it was literally nothing of any concern, and was benign,(and the fact that its been there 4 LONG years and not changed means its nothing of any significance at all - people without HA would just accept this as normal body wear/tear/changes)
Well, of course he should be trusted. What reason do you have to not trust him? Is your knowledge superior on medical matters? OR are you just naturally not wanting to trust him because of your HA, and that ever nagging doubt.