In my opinion, finding a scale fitting in a chord is a nice solution for jazz improvisation. Any scale or modes which does not conflict with the chord is a good option, even if you can not name the scale.
The scale you see in the video he used for A7#5b9 is aan A half diminished scaleAltered scale (thanks to Matt).
The concept of this video is, improvise a scale starts from the root of any chord, so, in you example, you have to decide improvising a scale on a I Maj 7 chord or a IV Maj 7 chord.
Say you want to improvise on a I Major seventh chord, and the chord is CMaj7, any scale fits [C-E-G-B] is a good scale, e.g., bebop scale on C , blues scale on A (but starts with C), lonian on C, lydian on C, e.t.c, are all good options.
You can also find scales matching on chords in this wonderful article - INTRODUCTION TO THE SCALE SYLLABUS.
I am learning jazz too, hope this helps!