Not really.

Inferring epoch from constellations is an old sci-fi theme and a topic that's discussed in basic astronomy classes. Considering the knowledge base and nature of this web comic's readership, I'd expect that this would intrigue and capture a certain percentage. (Smart people are smart and usually inquisitive...)

xkcd has a history of doing stuff like this. Take the "Dream Girl" comic, for instance. In one of its panels, it featured an innocuous set of coordinates and dates. As it turned out, they were a hidden invite for a meetup a few months into the future. Nothing about them was explained beforehand: it was up to the readers to figure it out. I've come to expect that every detail in an xkcd comic probably has some meaning.

http://blog.xkcd.com/2007/10/01/the-meetup/