“Cancer risk” can be a lot of things. It’s not like cancer is just one disease - it’s a whole family of diseases. The mechanisms by which something increases cancer risk are many and frequently poorly understood.

Fortunately, the mechanism of action of ionizing radiation and the cancer risks associated with it are well understood, and so we know that bananas are not dangerous.*

(* well, they’re not dangerous because they are radioactive. It could turn out that they’re dangerous for some other reason.)