One logical and probable reason for holding low would be that the tower may have been just about to open hence there may only have been a requirement of 1 pattern, not 100% sure.
Still, holding was carried out at 5000' which means a maximum of 170KIAS, requiring Flap 5 to be extended. At 6000', no speed restrictions imposed (including ICAO speeds) mean holding with flap extended. The basic fact of the matter remains, as mentioned in a previous post, for whatever reason the event occured, it dod occur and the crew were sufficiently trained to react to the warning and did so correctly, averting a more sinister outcome.