From what I see it looks like he was fired, as I read this
Brian Wilson Gone From WMAL - 5/19 - Breaking news late Friday: DCRTV hears that morning host Brian Wilson has been given the boot from Cumulus news talker WMAL after six years. Wilson is a former Fox News and Channel 5/WTTG reporter. More as we hear it.....
This would have been written by whoever did the article, and I wouldn't think that anybody that was given the boot, would have quit on their own. Which might be bad news for somebody that shares the same name as a member of the Beach Boys. Who come on, I couldn't resist saying that. I don't think you can say that somebody that quit on their own was given the boot, that would be at least strange to say.