Is the mūdra "little tarzan" a real thing? what does it mean?
It's most likely a Taoism's 手訣 (I'd say that the word 手印 is reserved to Buddhism). 
It probably comes from this book.
 
Apparently, there is a more famous 手訣 called 靈官訣, using by 王靈官, similar to 小泰山訣. 
Bonus: this is how it works in practice.

Source:

http://www.izhct.com/xiushen/dao/11095.html
https://kknews.cc/culture/5ojavp3.html
https://kknews.cc/news/6pgk2lq.html