It seems like this survey is about "outdoors activities" and not just activities that take place outside. For example, traditional sports like basketball, football, baseball, and soccer aren't listed in the outdoors section even if they take place outside. The survey is instead only counting activities like fishing, hunting, hiking, etc as outside activities. That will wildly skew the results.

EDIT: Here is the fine print of the survey:

>In this report, outdoor activities include adventure racing, backpacking, bicycling (BMX), bicycling (mountain/non-paved surface), bicycling (road/paved surface), birdwatching (more than 1/4 mile from home/vehicle), boardsailing/windsurfing, camping (backyard or car, within 1/4 mile of vehicle/home), camping (recreational vehicle), canoeing, climbing (sport/indoor/boulder), climbing (traditional/ice/ mountaineering), fishing (fly), fishing (freshwater/other), fishing (saltwater), hiking, hunting (rifle), hunting (shotgun), hunting (handgun), hunting (bow), kayak fishing, kayaking (recreational), kayaking (sea/touring), kayaking (white water), rafting, running/jogging, sailing, scuba diving, skateboarding, skiing (alpine/downhill), skiing (cross-country), snorkeling, snowboarding, snowshoeing, stand up paddling, surfing, telemarking (downhill), trail running, triathlon (non-traditional/off road), triathlon (traditional/road), wakeboarding, wildlife viewing (more than 1/4 mile from home/vehicle).