The link you provided appears to be an article combining ADS-b with Enhanced Mode-S. It has three sections and an intro. The “Track Angle” and “Roll Angle” information is in the Enhanced Mode-S section, and NOT the ADS-b section.
Are you asking about the data displayed for the other aircraft displayed on your ADS-b in? The above answer sums it up.
Additionally, ADS-b does not transmit attitude and heading information to other ADS-b receivers and ground stations. Any AHRS data calculated by an ADS-b unit is only for the use of the aircraft in which it is being used (ownship). Also, that info is not considered accurate for flight and navigation purposes. It can not be used except as a supplementary reference. Legally, it can not even be used as a backup to your TSOed, panel-mounted instruments. Although, in an emergency, something is better than nothing.
The information that ADS-b transmits is based on GPS data. GPS would give you the aircraft’s position (including altitude) and track (including trends) regardless of its heading and attitude. It transmits this information to aircraft’s airborne receivers and ground stations for rebroadcast automatically, without being interrogated.
An Enhanced Mode-S Transponder, when interrogated, transmits its information to ATC’s secondary surveillance radar. Along with its normal Mode-S information, Enhanced Mode-S can transmit specific Downlink Aircraft Parameters (DAP) when requested. This information is provided by various aircraft sensors. Some of these DAPs are:
- roll angle
- true track angle
- ground speed
- track angle rate
- true airspeed