you can find a lot of more posts where they mislead people into thinking whonix is insecure.
The whonix lead developer answered here: Secureblue for Default TemplateVM and Dom0? - #34 by adrelanos
If you read the whonix dev’s answer, you will see the non-surprising reason why GrapheneOs is saying such things: He had an different opinion on an highly technical non-whonix related topic (if you search the whonix forum you will find their discussion, it is an technically interesting read).
GrapheneOs often criticizes other projects for good reasons. But it is always a good idea to fact-check what they are saying, research the other side’s opinion / statements and to draw your own conclusion then.