Ask a few questions and you can still work out whether they actually learned it or just had it in class. Details depend on the curriculum in question, but recently when we faced this problem at a university recruitment a simple "Hey, what's a generator and why would you want it?" seemed to separate out the real learners from the classroom coasters.
Not that it really mattered that much, you still want to see learning of languages not in the curriculum and no 4-year program will ever cover all the interesting possibilities. We just learned that where "Java, C++, C, nothing else" is a warning sign from one university, "Python, C++, C, nothing else" was the warning sign from that one. You could probably generalize to "C, (Java/C++), exactly one other" and still be right.
However the main thesis holds true still... just replace python with haskell, erlang, clojure, or some other esoteric language.