That's a much more common type of lantaka. Most of the examples I have seen are in European museums and were traded or captured in colonial times. They seem to have been widespread around south-east Asia. I have examples recorded from Indonesia, Malaya, Brunei, Philippines, East Timur. There are always a large number floating round the internet, often described as Portuguese or Dutch rail-guns, often described as from a wreck in the Spice islands.
The characteristics of the guns which shows they are Asian rather than European are (starting at the muzzle) the flared trumpet -shaped muzzle with prominent sight; the two round bands at the muzzle neck; the bronze swivel yoke; the prominent "knob-sight"; hinges for a vent cover; the hollow cascable for the insertion of a tiller.
They are often, like this one, with the rear-half of the barrel facetted with triangular decoration on the facets and rounded in the front half. Some are facetted the whole length and some have twisted decoration on the barrels like candy sticks.
One of the differences is that no child could hoist a proper 16th century Portuguese swivel gun over his shoulder- they are too large and heavy- some are very large indeed!
But they do have characteristics which help you identify them. The details on this gun show that it is not Portuguese and not 16th century. On the other hand it does bear very close similarities to Asian Lantakas. In this case it is not the short length that is important but the very small calibre and the very light weight.