BCAAA is using NetServerEnum to determine which Domain Controllers (DC) are in the domain. This API gives us the NetBIOS name of each DC, but not its IP address. BCAAA has to lookup the IP address for each DC returned from this call.
Even though the IP address of each DC under [DCQDomainControllers] has been specified in the sso.ini, BCAAA still iterates over all of the DCs in the forest when it does DC discovery. Each time BCAAA finds a DC, it compares against the list in [DCQDomainControllers]. If the DC does not match, then BCAAA disposes it.
Note that the [DCQDomainControllers] can contain subnets as well as IP addresses. If a subnet is specified, BCAAA would still have to iterate over all the DCs.