Looking at scat singing, looked at origination of it, looked at Anita Day video where her phrasing was on the beat for a lot of it, The phrasing seemed more rhythmic. The video demonstrated large jumps in the scale while accenting in odd places.
Scatting is about varying the tone, using the scale, using the dynamics of voice and feeling free to switch words up and down round and about. It also sounded like the performance was taking other tunes and phrasing them over the tune the band was playing.
There is interaction with drums around 6.20, which to me is serious jazz. I heard Curtis Stiger do this at Le Monde in George Street Edinburgh back in 2012 and its very impressive. I have said it before but you really need to know your scales on this and have a strong understanding of the medley and the modes being used.
Billie Holiday and Lester Young
In this video you will hear sax play Eb scale and make good use of the blue notes and use the space that the band is providing. This track shows the importance of scale use and resolving if using dissonant notes.
Being adventurous will the melody is a good rule of thumb to stay away from being stale and predictable.