Tumors are basically cells that have mutated for some reason and begin to reproduce incorrectly. Malignant tumors begin to invade other cells and benign ones only stay unto themselves. (I hope that kinda explains it.) No, I don't believe a tumor could have been a result of a bite or tick. Ticks can transmit (through blood exchange) viruses, but it would have to be blood based and would be transmitted through the circulatory system.

I'd write down all your questions and take them to the vet. That way you won't have to worry about remembering everything, on top of the stress of the vet visit.