I don’t know, but I’ll put my neck out here.
Keying arrived in New York in 1847, went on to Boston in February 1848 and departed for the UK a month later. During this time in the States she was on display to the public (and also the subject of a law suit) so no doubt stirred some interest in this type of vessel. The vessel depicted can not have been Keying. Perhaps someone can say if a Chinese junk was seen in American waters between Keying, and 1920 with the arrival of the Amoy - I don't know of any.
I suppose the presence of a junk in America around the 1880s is possible, but a West-East Pacific crossing is no mean feat, and if one did, especially such a large vessel as this, it seems likely there would be some record of it. It seems more likely that the image was brought across from China, rather than the vessel. The artist had been a sailor in his youth, and may have been in the East and in a position to observe and make sketches of Chinese junks. After surviving a fire at sea, Johnson then trained to be an artist - and then later still, in the late 1880s, he travelled to Europe to study further - perhaps he stopped in Hong Kong on the way. Another possibility is that he could have had access to early photographs. Very few early photographs of Chinese junks seem to give the name of the junk - and even if the name of the junk is displayed on the vessel it is going to be unintelligble to the western painter and likely indistinguishable from the slogans and lucky charms which were typically painted on transoms (in Chinese characters.)
Unlike some early marine artists, Johnson appears to have known what he was looking at when he looked at a junk. This is suggested by the externally rounded planks, the mast parrels, and the sheeting system which shows clearly on the foresail. It is quite a lot more realistic and correct than the renditions which were made of Keying when she was publicised in the UK in the 1850s.
It is not quite right though – the large vertical bow transom seems unreal and somewhat impressionistic- and the exaggerated freeboard is typical of the way artists tended to render junks. On a more detailed level: There appears to be a confusion between a running backstay, and an aft lift/lazyjack, and it is interesting to note that although the main is hoisted to what looks like full height, the bottom panel is reefed, evidently not in the junk way, or by lifting the boom (which was sometimes done) but by brailing up the bottom panel to make it look a bit more like a western reef - which looks suspiciously like a figment of the Western imagination. Standing rigging was, of course, often seen on junks of that period.
All in all though, it does look like a surprisingly realistic painting of a junk, for those times when most western people knew little about them technically. It will be very interesting indeed if anyone actually knows the vessel.
A portfolio of Marshall Jonhson Jnr.'s paintings here shows that his style was romantic but also realistic and generally accurate, from small pleasure boats to large ships, some of which are valued at up to $US 7,000. Of 150 paintings the portfolio lists just two of junks (both in oils - this one appears to be watercolour).
For comparison: Victorian marine artist impression of Keying 1850s. Quite ridiculous.
Photograph of Amoy in the USA 1920s showing a bow transom.