Terrorism is an INCREDIBLY SERIOUS allegation. It should be dealt with by law enforcement and the courts. And the penalties for _false_ accusations, which is exactly what this is, should be severe as well. It can be life-ruining.
Terrorism should not just be dealt with through the courts. If you think someone is committing violence against others your responsibility is to shut down all support of that person, you mustn't aid them in any way. There's no requirement that private entities wait for the courts before stopping commerce with suspected terrorists. If you are google, that means completely locking out all accounts that you identify as involved in terrorism.
The supreme court has held that when making statements of public concern, you haven't committed libel if you are acting without malice. It's pretty clear google wasn't acting with malice here, and that it is a great public concern if someone is actually amassing armored vehicles to use against others. And just because someone is a terrorist, doesn't mean you should or can act through the courts. If google believes someone is acting against non-US nationals in a foreign country, then there's very little the US courts could pragmatically do about it other than order entities in the US not to support them. Of course if evidence did emerge that google flagged that terrorist activity was happening, and they continued supporting that activity, I don't think that would look favorably during any prosecution.
Which, yet again, brings me to my original point, which is that google shouldn't even be putting themselves in the position to scan private data and open themselves up to the liability of having invade privacy and to suspect someone is engaging in crimes.
"If you think". What if you're wrong?
So if you're wrong, you merely didn't engage in commerce with someone you believe to be a terrorist. There's nothing wrong or illegal about that. The agreement for free services by google doesn't mean google can't end the service at any time, and I'd bet the boiler plate for any paid service has a pressure release valve to end the service if google merely suspects you of engaging in illegal activity. In short, Google owes you nothing, and they're not your slave to provide you service despite believing you're a criminal.