I would think that a fan that has the purpose of cleaning the filter would have to blow in the reverse direction to blow the trapped dirt out. It would probably be on the clean side of the filter in that case, and any shrapnel it spewed off would go right into the turbine inlet.

It's likely drawing bypass air.

Here's a prefilter for a tractor or something:

https://www.youtube.com/watch?v=_P3u7wgiy-c

It's using air flow to blow the particles out before they hit the filter. If I understand correctly, the part in question does similar, pulling debris out of the intake stream without being in series with it.