It's Counted Far Too Many Floors
Some Fitness Trackers allocate "Floors" to your daily activities as a measure of increased activity (its harder to go up stairs than down). To detect if you have "gone up" they measure atmospheric pressure, which reduces as you go up and increases as you go down. If the tracker reads steps it thinks you are walking/running, and if air pressure reduces, it assumes you must be climbing upwards and so allocates Floors to your daily stats.
However, air pressure can change for other reasons, most noticeably when we have windy days. on windy days, the devices can be fooled by changes in air pressure caused by the windy conditions and can allocate Floors that have not been climbed.
Unfortunately there is little that can be done to cancel out this effect so its just a case of recognising that its not a fault, just a quirk of how the systems work.