Means the same as the phrase, "just to be sure"; the "it's Westinghouse" part originated from television commercials for Westinghouse Electric in the 1950s, who's catchphrase was, "You can be sure, if it's Westinghouse".
{Craig}: Hey Paul, did you remember to charge your wheelchair today?
{Paul}: I think so but let me check just to be sure it's Westinghouse.
It happens when an individual drinks too much and then acts and assumes they are really importnant with anyone that they deal with. This drunk person tends to overstate who they really are.