Lowell interrupted the caller and explained as clearly as he could, that he could not allow the caller to continue. That he knew what the caller was going to say [about Islam]. That he knew what the caller had to say [about Islam] was likely true.
That the station would likely be heavily fined, the host may well lose his job but would certainly be reprimanded for allowing the caller to continue, and that the consequences to the station and staff overall would be greater than the station could bear.
That the caller should feel free to trash talk Judaism, Christianity, Hinduism or Buddhism but nothing may be said of Islam that may make it look bad, even if true.