It peaked at 4.05% in March. The last 2 months it went just below 4% as the Unknown category increased. For June the reverse happened, so 4.04% seems to be the real current share of Linux on Desktop as desktop clients were read properly/werent spoofed.
For some reason I think a lot of them (probably even more than half) have tried browsing the web or at least using the desktop mode at least once.