Emergency presidential alert texts could be faked, researchers say June 20, 2019 https://www.cnet.com/news/emergency-presidential-alerts-could-be-faked-cu-boulder-researchers-say/
Oops. Somebody didn't think things through. But then, it's a legacy setup, with ad hoc internet/cellular add-ons.
Apparently yes. "Researchers Send Fake Presidential Alerts to Stadium of 50,000 Using LTE Vulnerability..." [Same research report as OP] https://gizmodo.com/researchers-send-fake-presidential-alerts-to-stadium-of-1835806990