TTF format, confused

When I read about the .otf format, they always say it provides benefits like larger character sets and ligature/small-caps/etc, features...referred to as "Opentype features". I stayed in this otf world, scripting and utilizing these features for years.

So in an effort to delve into ttf hinting...imagine my surprise when I converted an old .otf into a .ttf, installed it, and saw ligatures I made were still accessible in my Adobe apps. What's going on? I thought those Opentype features were exclusive to the .otf format? Someone set me straight, please.