How BV can apply row filter for Users in an instance

I just found a great function, which cannot be replaced by any other BOBJ Products:

If the crystal reports is based on Business View and sets row filter to a BOUSER Group, we run this report in BOE platform with Administrator, but when the BOUSER Group logon in to view the report instance, they can still view different row filtered data.

While in our other solutions, we can only schedule for this BOUSER Group, then we can see multiple instances for every row filter.

In my understanding, instance is static, why BV can apply row filters for Users in an instance. In our document, it says BV row filter is applied in Processing Extension. Any one can help to explain the processing flow?

Thanks in advance!

Jennie