I had a colonoscopy and they did a biopsy and it came out : colonic mucosa with reactive lymphoid hyperplasia. what does this mean?

It means you have no: This means, no cancer was found. Lymphoid hyperplasia has no particular significance in this site . So you have no need to worry about cancer or anything else based on this biopsy report. Which is benign.

Not a true polyp: The goal of colonoscopy is to prevent the development of colon cancer, a process that takes 10 years from the start of a polyp. A small bump was seen that may have been an early polyp, but on biopsy it was only a lymph gland- nothing to worry about! good news! no polyp.