Did my dog die from moldy food?

Hello, hoping to get some insight on my situation.

I had to put my dog down about a month ago after an emergency ultrasound showed late stage cancerous growth in his abdomen. He was otherwise very healthy (a full check-up 2 months prior had confirmed this) and relatively young at 6 years old. The vet wasn't clear about what type of cancer it was (or maybe I was too distraught on the phone and just missed it) but when I asked how it might have happened, he said genetics and/or bad luck. That's the story I've been going with.

However, just yesterday I was finally cleaning out his food container (one of those big Tupperwares made for kibble) and at the very bottom of the bin I found a roughly 2" chunk of moldy kibble. I immediately googled this and learned about mycotoxins, specifically aflatoxin and how it commonly grows on dog food, especially kibble. The moldy bit may have been in the bin for as long as 2.5 years, as I typically refilled the bin straight from new bags before running empty. My now strong suspicion, as much as I hate to think it, is that I slowly poisoned my dog over 2.5 years and that's what led to the cancer. Can any vets shed some light on this? No need to spare my feelings; I've already beat myself up about it and now just want to know (and want others to know) in order to do better in the future.

TIA.