Ling Guangzhao wasn't boasting. As a native Beiping child and the current boss of Babaozhai and its former young master, he indeed knows Xia Mubing well.
As to how familiar he is, and how much Xia Mubing appreciates him, that's pure boasting. In Ling Guangzhao's description, as Xia Mubing grew older, his temper became increasingly eccentric. At least when Ling Guangzhao was a child, Xia Mubing was much easier to talk to than now.
Ling Guangzhao even played in Fen Garden as a child.
Fen Garden, regarded as Beiping's top private dining, is essentially not a private dining restaurant, but a complete, grand three-entry courtyard. The part open to guests is merely one entry, while the other spaces are where Xia Mubing and his disciple Zhang Guanghang live.
