It's the most obvious example, it's not the sole piece of evidence.
Let's pick through the official statement.
"In addition to carrying out anonymous telephonic threats, these devices could be used to conduct a wide range of telecommunications attacks. This includes disabling cell phone towers, enabling denial of services attacks and facilitating anonymous, encrypted communication between potential threat actors and criminal enterprises."
This is a mix of bullshit and mundane. Disabling cell towers? I don't buy it. DoS attacks? Yeah, any collection of internet-connected devices can do that. Anonymous, encrypted communication? Everybody's smartphone qualifies for that. You could be talking about arresting a pickpocketer and be technically correct in saying that you siezed a device that could be used to facilitate anonymous, encrypted communication between potential threat actors and criminal enterprises.
"While forensic examination of these devices is ongoing, early analysis indicates cellular communications between nation-state threat actors and individuals that are known to federal law enforcement."
So some foreign government was using these services. You could say the same about AWS.
"The potential for disruption to our country’s telecommunications posed by this network of devices cannot be overstated"
A nice example of the genre of self-disproving statements.
"These devices were concentrated within 35 miles of the global meeting of the United Nations General Assembly now underway in New York City."
It bears repeating that "within 35 miles" of the UN includes the entire New York metro area and a large area beyond. In addition to that, the very concept of electronic equipment being "concentrated within" four thousand square miles doesn't make the least bit of sense.