Yes. Answer is 100% correct. If configured VM-Host affinity/anti-affinity rule is MUST, it can not be violated. Even vSphere HA honors the VM-Host must rules. Even you can not manually migrate that VM1 to other Host. Maintenance mode also can not evaluate the host. Even if there is CPU/Memory imbalance, DRS will still obey this rule.
If you want this rule to be flexible, then you can configure the same as "soft/should" rule. In this case, rule will be violated whenever it is absolutely required(like MM, HA does not honor this rule, you can manually migrate that VM to other, DRS for the sake of balancing cpu/memory can violet this rule) But note that in the immediate next invocation of DRS, DRS will try its best to resolve the rule violation.
To know which rules can be honored by vSphere HA :is vSphere HA aware of DRS affinity rules? | vThinkBeyondVM
Let us know if you need any other clarity.