I think u/Katamirand was referring to the "mistakes" in DNA replication during cell division. You should know that there are double-stranded DNA viruses that can infect and survive in the nucleus of the host cells while there are other viruses that have single-stranded RNA. In short, the polymerase in most RNA viruses cannot repair replication errors so these errors would be causes for mutations. So it's not so much of 'what the host cannot provide' that causes replication errors/mutations, but just think of it as a natural occurrence that not only can be caused by a multitude of factors, but also simply just by chance.