when Yibo knew Xiao Zhan, he was still young and was treating XZ as his big brother. His mistake was not realize that XZ did not receive training with him for a few years like his other friends from the Uniq, so, XZ could misunderstood the closeness Yibo showed him to be more than brotherly love, xz worried about it and he distant himself from Yibo. That hurts Yibo's feelings.