The virus described here was first engineered by directed evolution, and then genetically modified with additional functions. The virus doesn't attempt to modify the genome of the human patient.
The clever trick is that these viruses are programmed to target cancer by engineering them to not be able to survive in non-cancer cells. In the case of ColoAd1, the virus will be destroyed by the p53 found in normal cells, but missing from cancer cells.
Engineered viruses might also be evolved or engineered specifically with a kill switch mechanism or be selected to be highly sensitive to a particular antiviral medication.