Nothing comes from nothing, so for the Yangs and Wu brothers to have concocted Taijiquan (according to the Heretics Hypothesis) it must still have been made from Yang LuChan’s genuine martial skill. The postures of Yang style share a lot in common with various Northern Chinese martial arts. Changquan (long boxing) is often quoted as something Yang LuChan practiced in childhood, but again, this seems to be purely anecdotal. That doesn’t mean it’s not true of course.
A martial art popular in the region Yang came from was Hong Quan. A video surfaced recently that showed some traditional Hong Quan. It’s interesting to watch because I think it’s a good example of the type of martial art that would have been around at the time of Yang LuChan.
The description offered with the video says: “Here is the Xiao Hong Quan of Mogou Village. Mogou is to the east of Dengfeng and has practiced Hong Quan for hundreds of years.”
Hong Quan was very popular during the reign of Emperor Daoguang, which would be the Emperor immediately before Xiangfeng, who was emperor when YLC went to Beijing in the 1850s.
Out of interest, at a cursory glance I can see at least four Tai Chi Chuan techniques I recognise in that Hong Quan form presented – wave hands like clouds, snake creeps down (low single whip), bend bow to shoot tiger, and lotus kick. It’s hard to spot because it’s quite fast. But I’d hazard a guess that you’d probably find those same general techniques in lots of northern martial arts, like Chang Quan, as well.