Some backstory: Originally, Amtrak provided its GTFS feed exclusively to Google. That was unfair, so someone filed a Freedom of Information Act (FOIA) request to get the feed released to the public. Amtrak technically isn’t a federal government agency, so its works aren’t automatically in the public domain. However, they are subject to FOIA under a special law that gives the public a right to inspect their records, which is orthogonal to copyright law. I don’t know if we can assume the resulting records are in the public domain, as we would with other FOIA requests.
Transitland originally included a link to this FOIA’d feed in a combined DMFR file that itself is under CDLA, alongside links to other feeds that are under a variety of licenses. The “license” of the Amtrak entry simply linked to the FOIA request, which isn’t much help. A year ago, Amtrak began publishing a public GTFS feed on its website. Transitland responded by splitting the entry into a separate DMFR file, retaining the CDLA license on the DMFR file. I don’t think that has any bearing on the rights around Amtrak’s feed.
The California Integrated Travel Project was apparently involved with getting Amtrak to publish this feed. CalITP is a state government initiative whose works are automatically in the public domain, but I wouldn’t assume they actually authored this feed.
That’s a lot of words for me to say I don’t know. 
But I don’t think it’s under the CDLA. If you’d like a more informed answer, perhaps you could reach out to Transitland on their issue tracker.