I think he clearly snorted too much white stuff today. It's a simple alert.
I think both of you are correct. The alert itself is a simple one-way broadcast, according to technical documents (if they are to be believed). But the feds certainly CAN remotely access everything on your phone. Edward Snowden's leaks uncovered a lot of that, and there must be much more that we don't know. So while the two (may or) may not be related, what nutjob McAfee tweeted is something that's within the government's abilities.