I also have the same issue.
Just got the survey for the first time in a few years (always running Linux), same issue. optirun glxinfo has no problem seeing the card. Considering other issues (many users pointing out they never got a survey on Linux), it seems like the survey might not be reliable
See also this thread.
Nothing extracted yet.
Because I wasn't running Steam with optirun when I was invited to the survey (I'm using launch options for specific games, rather than running the whole application this way) the survey concluded that my only card is the integrated Intel card. Maybe the survey should scan for launch options for the use of optirun, so that it knows if someone uses bumblebee with his nVidia Optimus card.