The A/I vetting was in the form of a form asking why do you want A/I email or blog. You could write anything in it.

Meanwhile, Signal requires a phone number, so it knows much more about your identity than A/I did.

How do you know what the A/I vetting consisted of or what standards they held? They don't seem to have published any detailed description of the process, and by their own account they destroyed all records of the vetting after approval.