Nailed it.The 1st Amendment protects individuals from being prosecuted by the government for expression and speech. It does not protect individuals from the consequences of that speech, nor does it guarantee that the speech is heard, disseminated, etc. In this case, theater owners and ultimately Sony Pictures made a business decision. This has nothing to do with free speech or the 1st amendment. Lots of people seem to be confused by what the 1st amendment is and what freedom of speech means.
Now, to your point, one could argue that the USG has a duty to protect citizens, corporations, etc from these kinds of attacks/threats of reprisals... but it's not a free speech issue.
You're right it's not a first amendment issue. It's a pussification of America issue.