I would say that Ab pentatonic was Ab, Bb, C, Eb, F, and Ab - a subset of Ab major. It is very odd to talk of an Ab flat scale and then refer to a set of notes that do not even contain Ab.
It is a habit that I have seen fairly often with guitarists but rarely elsewhere to only ever talk of sharps e.g. always refer to the note between A and B as A# rather than Bb. If you move into the theory of music, you will find this habit an even greater problem. For example, if you say that the F major scale contains A# then it will be considered wrong even though it contains Bb.
Back to your problem. Your set of bass notes do not even overlap your piano notes at all. In fact, they are a semitone away from the piano notes. I would expect Eb on the piano with E on the bass to sound pretty bad. The simplest explanation is that one or the other instrument is out of tune. If both sound okay individually then they may be in tune with themselves but one or the other (or both) is not in concert pitch. It is a bit more likely that the guitar is out but it could be the piano. How do you tune the bass? If it is with a tuner then that points to the piano. If the piano sounds okay by itself and you want to play the guitar with it then tune to the guitar to the piano not the tuner. It is not so easy to change the piano so accept when it says that Eb is and match the guitar to that.
Consider getting your piano tuned. For quite a while, my piano was relatively in tune but consistently a semitone flat. Since I don't have perfect pitch, I could live with this for piano solo music. It also worked with voice. It worked with guitars provided that they were tuned to the piano. It was an issue with some instruments such as the clarinet and saxophone.
Finally, it is very common that a tune does not start on the key note. Many tunes in C major start on G. It is more common, but still not certain, that they end on the key note. Determining the key requires a bit more theory and, for some tunes, there may be no definitive answer.