Descending while turning inbound on a non-precision approach
It's because 2500 feet is the minimum altitude prior to starting the inbound descent at 8 DME and you can descend to that altitude pretty much anywhere between ABV and 8 DME inbound, within the protected airspace of the procedure turn.  

When you started the outbound leg at 3000, you can pretty much descend to 2500 sooner or later, as long as you don't descend below 2500 until you are 8 DME inbound on final.  So if you find yourself at 2700 at 8 DME outbound and you're ready to turn in, you can keep descending to 2500, leveling at 2500 until you cross 8 DME inbound.

Basically, the airspace between ABV, the 10 mile circle, and 30 degrees of the approach path is the protected airspace with a floor of 2500, and technically, you can do whatever you want within that zone.  Also the altitude is a minimum.. you don't have to descend to exactly 2500, technically (I'm assuming SA IFR rules are similar to NA)