In this context, it may just be an intended Eb chord, the player hit the open E string by mistake and thought 'that sounds nice!'
Chords don't HAVE to come from one scale. A common one that doesn't is the 'Hendrix' chord, a dom7 shape with the minor 3rd on top. (Theorists like to call it a #9, your ears will tell you it's a b10.)
However, when a chord is in general use, and has an accepted name, the jazzers generally WILL have discovered (or invented) a scale that fits it. They like a chord symbol to imply a scale.
Don't worry over esoteric 'slash chords' though. They might just indicate a pedal note. C, Db/C, D/C, Eb/C etc. is a common trick, and you can leave the bass note out of any 'chord=scale' analysis.