Correct Cast Order!

I haven't seen this particular film, but it is quite likely that the IMDb sequence is accurate.

As noted in the Submission Guide: Order :

Acting credits are ordered according to the most comprehensive cast list (the one listing the most actors); in most cases, this will be the list appearing in the end credits.

and

We are aware that casts in order of appearance or alphabetical order sometimes mean a lead actor is buried relatively deep in the cast list. This is somewhat unfortunate. We do have a separate system for indicating the lead actors, but it is not yet in widespread use through the database.

As I said I haven't seen the film, but looking at the IMDb list, I expect that the on-screen credit roll was ordered by appearance.