Response headers mention an onion-location and link to stolidityseashellshotter... but also mementoweb... pretty strange. Most generously, maybe some kind of cache poison instead of explicit bad behavior?
This looks like some kind of misconfiguration more than intent, or a mix, but it's still bad.
Edit: It sure does seem to be a PDF problem, these were both NYT things, but I tried a CCC talk page that had a slides link and sure enough, same behavior.
https://archive.ph/o/n5qxb/https://fahrplan.events.ccc.de/congress/2015/Fahrplan/system/event_attachments/attachments/000/002/825/original/32c3-slides.pdf