Well, no, that isn't the official definition. The official definition is it has to have at least one RealTrack.
I somewhat disagree. The user manual states that RealStyles are Band-in-a-Box styles that use RealTracks only (and the file names are prefaced by an underscore). However, it goes on to call the styles with one or more Realstyles, "Styles with RealTracks", which are a blend of MIDI tracks and RealTracks. Style names for Styles with RealTracks are prefaced by an equals sign.
That definition may have changed, but that is how it appears in both the BIAB 2017 and BIAB 2018 user manual.
And of course, hybrid styles are "user" styles created by combining the various track definitions of multiple styles into a new style file.
Yes, it does get very confusing.