They didn’t say that at all. They said the standard Colorado is using to convict people is too loose, and could theoretically be used to restrict constitutionally protected speech. They were not ruling on merits on if this speech is protected or not. It probably isn’t. Now the case has been sent back to Colorado, not closed. Colorado can retry him, and it’s quite likely they would win even under the stricter standard. But they can’t try him under a loose standard that could allow for protected speech to be criminalized. This has very little to do with the actual case, and a lot to do with the law that Colorado was using. Most articles written about this are lacking in information and misleading at best, you could find better information on the ruling on scotusblog or the ruling itself.

Among Counterman’s communications to Whalen were messages that read: “Was that you in the white Jeep?” and “You’re not being good for human relations. Die. Don’t need you.” Others used expletives.

Counterman, citing mental illness and delusions, argued that his messages were not intended to be threatening and were thus protected speech.

Not the guy you responded to but god damn… I can’t see that message being interpreted as anything BUT a threat. All I gotta do is declare insanity I guess.