Worcester 1947 gives the attached (approximately 1350s) description of topsails. My guess is that they were more commonly used when cotton sails replaced mat sails.

The photos are the first documentation of the use of jibs and topsails (Worcester mentions a model in the attached article. Sea-going junks are almost completely undocumented for a number of reasons which is why current underwater archeology is so important. Almost all of the documentation of junks and their rigs is from waters with restricted navigation in estuaries and trade in locally used goods in contrast to offshore trade with high value or perishable goods. The photos challenge a lot of the dogma/assumptions about the junk rig and its use.

It is common enough to see photographs of Chinese junks in Hong Kong and other ports under the influence of Western countries, with rigs which included technology borrowed from Western ships - for example wire standing rigging.  Photography (and the publication of photographs in print magazines) was becoming popular by the end of the 19th century and the beginning of the 20th - the very same period in which a number of Western powers were enjoying seized territory, and influence in China. This might also explain the triangular sails which can be seen set flying in the two photos from China, even though these "kites" are not found in the literature on Chinese rigs. That would be my explanation; interesting but not really so surprising.

As for the Japanese boat with its bowsprit and tiny staysail - an interesting mystery.  

Japan did not invade China in this period - although it did seize and occupy some parts of Manchuria and Shandong Province, and was in control of some German territories in the far east of China (for example Qingdao) in 1916.

Japan always had its own tradition of junk rigged boats, so there seems no reason to suppose that the Japanese junk photographed in Nagasaki had originated from China. More likely just a local boat - but the bowsprit and staysail is interesting. There had been a US Consulate in Nagasaki between 1902 and 1912, but that had closed down by 1916. There was no American military presence there in 1916. What was the USQT Sherman doing there in 1916? My A.I. is guessing this was the USAT Sherman, a transport ship, stopping over for some, now unknown, reason. Nagasaki had a major coaling and repair facility there. Perhaps the Japanese junk with its bowsprit and tiny staysail is just evidence that Western rigs were known, and "messing about" with boats is a universal pastime. It's an interesting photo.