If my doctor takes a biopsy during my colonoscopy, does that mean that he found a cancer?

No. Something he saw needed clarification.
No. Biopsies are taken for many reasons. A biopsy is a sample of tissue used to help establish a diagnosis. It may show inflammation, a benign polyp or growth, infection, parasites, or it may indicate cancer. Just because a biopsy is taken does not automatically mean there is cancer.