I hear what you’re saying, but i have definitely borrowed an iphone, gotten an incoming call, and seen that big “hang up” icon (you would say decline). Since none of the buttons seemed safe while my attention was on the call (did not parse the “decline”), I’m pretty sure I just ignored the whole acreen until it went away.

If you are used to iphones and “incoming call” screens, I’m sure it does not confuse you, but again, it is not a universal design.