First, was your film x-rayed? I.e., you were traveling, you went through an airport or two or dozen, and now you're developing the results. If not, then probably that's not from an x-ray machine.

The pattern doesn't look like x-ray damage, and it doesn't look like a development light leak. I can't imagine a camera doing that. It looks like something horrible happened at Kodak.

(Oh, BTW, welcome to the forum!!)