How so? If you kept a disposable VM open and just created new identities in tor browser, how does Qubes mitigate the threat here?
On Qubes, you do not create a new identity in the same VM. This would go against the Qubes approach to security/privacy. Using separate VMs for independent tasks is the whole point of using Qubes.
I believe you are correct, and that this poses a significant risk for people who don't properly understand the underlying concepts.
A Qubes OS user needs to start a new disposable Whonix workstation VM to sidestep this attack, NOT create a new identity in the same disposable VM's browser, which is exactly what this attack targets.