The hinged and tabbed triggers on modern striker guns are to keep the trigger from moving rearward when not being engaged. They are NOT manual safeties of any sort, and it's ONLY to prevent movement of the trigger due to inertia.
It's been a long time since I have had access to a P320 so I can't comment on the "how", but the P320 was designed internally in such way that it does not require a physical block of the trigger in order to keep the trigger from moving.
Sig made the tabbed trigger safety only because some contracts and some individuals require it simply because the trigger safeties are so prominent some will never feel comfortable without it (like some people with manual safeties or grip safeties).