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Hi Tony,
I wouldn't worry too much about the difference between the two.
Why?
Because the polar alignment process takes into consideration any misalignment between the camera and the mount whilst the astrometry solving only looks at the alignment of the camera and where it's pointing.
Polar alignment involves (usually) three images at different angles to calculate where the centre of rotation is - which is where your mount will be rotating about.
An alignment error of 40 arc-seconds is quite good, and for your focal length (at most 55mm) any error will not be noticeable in your images.
I hope this makes sense - it makes sense in my head as I type this...
Cheers,
V.
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