Ah....the old "half step off" gremlin strikes.
I think we have all done that at some point in our playing careers if we have played out live quite a bit.........but the difference is most people notice it within the first one or two notes.
Neal is a good player though, I'm sure he couldn't hear what was going on.
That look on his face when he looks at the fretboard and moves up a half step is priceless