The way I analyzed -- I did think about it briefly -- is as follows:
Scout was asking Yoda how he was aware of a piece of information.
Being that Yoda is supposedly super smart and all knowing, he states who he is and his credentials, then sarcastically asks Scout if it is by random chance that he is Grand Master.
Why would it be funny to some?
Two reasons:
1) I would guess that in a work setting (Grim’s workplace), it reminds a manager/higher-up (as Grand Master) what he/she could tell a rookie (as Scout): that it is more than just chance that got him/her to be where he/she currently is. (Possibly, when reading it, other coworkers came to mind with the same symbolic roles as the story.)
2) At another level, just the way Yoda talks is funny. [EDIT: I just remembered that I have also heard Grim say, "me thinks," so he likes that kind of weird talk

lol]
OK Grim, was I right on my first part?
Grade my literature skills.