As others have said, this indicates to me that a higher than expected number of game designers are starting their dreams while still in school. Either some number of the survey responses are from people who got lucky and dropped out, or got lucky, and might -currently- be in school (that qualifies as 'some', right?).

I seem to recall that in the late 90's, just before the tech bubble popped, it was a popular thing to drop out of school and start working for a game company.