I doubt you will ever know what caused your cancer but it's VERY clear that smoking can cause all sorts of cancers including oral so the easy part is to eliminate that from your list of cancer concerns.

We do see many, perhaps 1/3rd of the people that have come here say within the last 6 years with a Dx of oral cancer that are neither HPV+ nor smokers and so far no one in the scientific community has offered an explanation.

Try not to beat yourself up over having the cancer, million and millions get cancer. The most important job now is to focus all your energy into doing everything possible to rid your body of these maliginant cells. I'm certainly not suggesting it's easy to brush aside all these negative thoughts popping up in your head right now but just realiize this is a normal part of the progression we all have to go through and the sooner you get past this stage the sooner you can focus on the real important stuff like curing you.