Excellent questions. Going from memory, I'm confidant that the judge expressed to someone that the subpoena simply didn't apply and/or was unconstitutional.
I assume that meant that the subpoena came to him through some route.
Let's go at it this way. My understanding is that the Congressional committee issued a subpoena to Terri (probably directed to husband as guardian of her person) in an effort to trigger a criminal statute which punishes 'harm' done to witnesses under Congressional subpoenas. It was hoped (by the issuers) that this would dissuade doctors from removing the feeding tube. I further understand that the subpoena was not properly served, but was mailed to someone.
Contempt of Congress comes in ignoring its lawful order. Usually, with a subpoena, that means 'appear.' If you fail to appear, enforcement is through a contempt citation.
Clearly, the judge could not be guilty of contempt (nor could anyone else save Terri). He wasn't ordered to appear.
By the way, the premise of the whole endeavor begs the question. Was pulling the feeding tube really 'harming' Terri? Was it done at someone else's direction or at her own, judicially-determined direction? I think the relevant Congressional committee would like to forget the whole thing.
What about the criminal statute? I don't know the statute so we are really flying blind here. I don't know whether it requires the witness to have been lawfully served. I would guess it would, otherwise, they wouldn't really be a 'witness'. Lots of problems here and I doubt anyone would want to try to enforce it. It was mostly a PR ploy in my view.
I did hear some windbag pounding the virtual table about subpoenaing the judge to testify to a Congressional committee about the basis of his ruling. I would suspect every judge in the country -- state and federal, right and left, Republican and Democrat -- would unite as one to oppose that on separation of powers basis. What an awful precedent.
Much ado about nothing.