Hi Michael,
Interesting find as usual. Lovely firearm and workmanship. Unfortunately the view is clearly limited.
Try as I might I am unable to find any single element that would enable me to definitely agree with a Cingalese origin. Similarities are there of course but since the view is limited, it is difficult to come to a clear conclusion. On the other hand the winged humans, scales in hand and the type of lions on the under side of the stock ... do they suggest a non oriental origin particularly, European?
Interestingly, Arne Hoff in Dutch Firearms identifies a wheel-lock with a shell shaped design on the lock as a Dutch Firearm. See color plate II.
Regards.
P.S. Now you'd better make sure your flat is not bugged too.