Without knowing the internal workings on the patch I can only guess, but...
Both IE and IIS support versions of TLS that are not vulnerable to BEAST, e.g. TLS v2 and v3, but these versions are not on by default. Also, it's dependent on the cipher suite used in the connection for v1. The patch could do a number of things like turn the versions on by default, or disable the particular cipher suite that is vulnerable to BEAST.