How does this definition of sunnah relate to its broader use in hadith studies?

Prescribed Acts and Prohibitions: Fard, Wajib, Sunnah, Nafl, Haram, Makruh, Azimah and Rukhsah

• Every reported saying automatically counts as an emphasized sunnah
• Both concern only non-legal social customs
• Hadith scholarship never includes sayings under Sunnah
• Here it is a narrower legal grade; in hadith studies it includes sayings, actions and approvals