The Mythicist position- pretty much what the article describes- is almost the opposite of historicity. Mythicism essentially states that the person in questions' existence isn't the issue, but rather the myth was built from previous myths and needn't be attached to a person. We think as you indicated that some person like a Joseph Smith or Jim Jones was turned into a deity, but that needn't be the case. It is possible to invent a messianic/martyr figure out of whole cloth because religious literature was already full of them.
One big example is the legend of Romulus, founder of Rome. I'm going to do a comparative thread on that soon, but basically he fills the shoes of Jesus quite nicely. Just turn Romulus into a Jew and you have Jesus. There are many orther examples that have been posted on here, like Osiris. Because Christianity began in Rome, the Romulus figure would be a very appropriate one to build on.
Another thing to emphasize is that, up until recently, Christian historians were writing the books and doing the research. Key point being the conclusions they came to varied widely, and maintained belief in the existence of a historical figure. Mythicism says not necessarily so.
This, for your perusal.