It certainly looks like a banjo, unless he's carrying around a bedwarming pan or a giant bath brush.
To be plausible I think you'd need to paint this figure as a West Indian. Wikipedia says the first white banjo player was Robert Mcalpin Williamson, born about 1804 (link below). That the banjo was first played on stage in the 1830's, and that the instrument was introduced to Britain by a minstrel group in the 1840's. But it was a Carribean slave instrument dating back to the 17th Century.
https://en.wikipedia.org/wiki/Robert_McAlpin_WilliamsonI think a feature that identifies a figure as being a West Indian recruit is pretty cool, even if it's not wholly accurate.
Banjo aside, these are very nice looking figures. Standing figures are notr my favourite thing but still, verry nice and usable.