Think of BVI the same as a SVI in a switch. It brings the layer2 information into layer3. With BVI, you can have multiple interface running layer2 (bridging) sharing the same L3 subnet. BVI interfaces are often seem on Integrated Routing and Bridging (IRB) implementations since you need to route and bridge at the same time.
As for your access point, it's using BVI to bridge the wireless radio interface with the LAN interface of the AP unit, making it one seamless network.
