It looks like a connection check whereby the bolted connection angle is trying to peel or pry off the face of a girder.
This might be the case if your clip-to-beam connection has no rotational stiffness and you need to rely on the fixity of the clip angles to the girder to keep the connection stable.
The calc seems to assume a rigid connection angle.
See 7-10 in the fifteenth edition of the AISC manual for the current methodology.
