I do not think it is a normal thing to do. Like another poster stated, if the company can afford to do a four hour lunch for almost all of it's staff, but one, then they could have hired a temp. for those few hours.
I don't think that they meant it personally towards your brother though, as in, he is not doing a good job. The company appears to be just clueless in how to treat all of their employees. And, I think, they just went with the last person on the totem pole, so to speak, in regards as to who would man the reception desk.
What they should have done was just close up shop for those hours. Would they really lose that much business?
Also, I sincerely hope that someone brought something back for your brother from the luncheon.
Would I look for a new job? Possibly.
Would this leave a bad taste in my mouth as their employee? Most definitly.