Speedtest wired versus wifi

This one seems weird to me. I have a MaxBR1 with a cable modem WAN connection. If I do a speed test (www.speednest.net) from my Macbook Pro via wifi, I get 20Mbs download. When I check the speed through the Apple TV Speedtest App, I get 68Mbs download. Tested this many times and although the speeds vary a bit, the gap is still huge.

Any ideas what this could be?