Can your colon cancer come back after 5 years of being in remission?

Yes: A majority of colorectal cancers, if they recur, recur within 3-5 years, but it is possible to recur later as well. The other possibility is development of new cancers or polyps, which is why surveillance/screening colonoscopy may be warranted. Ask your doctor/surgeon for more information.

Yes it can, rarely: Late relapses(after 5 years) are uncommon but not unheard of. So it is not a total surprise.

Yes: Yes. Any cancer can come back at any time. Cancer doesn't listen to doctors or textbooks very well. However, for most cancers, including colon cancer, being 5 years out ned (no evidence of disease) is a practical definition of cure. Likelihood of recurrence is low.