Looking at the wiki for Wonsulsa, it seems to be something like a title you have to take an actual exam to earn.

[quote=ToG Wiki]
In order to become a Wonsulsa, one is chosen to take certain Tests at Gustang's Research Association to become certified. Because of this, there are few Wonsulsa as only those who have passed have learned this technique. Requirements to be chosen to take the test are currently unknown and it is also unknown if Regulars are allowed to take this test.
[/quote]

So it might be a case of having similar abilities but not officially being recognised as one.