What law requires them to keep genetic information?
I don't know. I do know that I used their process to delete my data (and account), and they claimed they complied. Whether or not they did, I have no way to know.
I wonder, though, if what they're talking about is that they have to keep the data as long as you have an account with them. The fact that you can't delete your data and keep your account hints that may be the case.
What is your threat model or the risk you are attempting to mitigate?