I just had a thought on this yesterday that brings a logical explanation for his belief. First of all, saying it "causes tumors" makes about as much sense as saying you'll "catch AIDS". I'll assume he meant "causes cancer".

Anyway, if this wrap is grape I'll assume it's purple. Purple would be a mix of red and blue colouring. Red dye often contains Monosodium Glutamate, which is carcinogenic. So yes, in theory it could cause cancer. But then so could red candies and chinese food, both of which have been linked to higher incidences of bowel cancer.