Nice piece but IMHO the decoration is mid to late 20th century, and typical of Yemeni work. Likely white metal rather than silver. The matchlock gun could be older. I would call the style Indo/Arab, and agree that it probably originated from the Hadhramaut region.
It looks to be complete, though an old break in the stock is evident. The older piece of iron/steel band over the top of the comb of the stock is to strengthen the repair. The white metal decorated plate shows no damage and this is why I say that this decoration is a later (and more modern) addition. Also the wound banding down the barrel is not usual, and is likely to enhance "eye appeal" at point of sale.
Similar matchlock style from Oman at this link
http://www.vikingsword.com/vb/showthread.php?t=18302
and here
http://www.vikingsword.com/vb/showthread.php?t=18832
Stu