The man portrayed in the painting with armor and a golden spear was, of course, Sirius. This was an unmistakable fact because right in the sky two wide-open wolfish eyes could be seen gazing at the world below; very similar if not identical to the Wolf Emperor's Domain in Bai Zemin's possession.
In reality, Bai Zemin only revealed that he might be the man portrayed in the wall art after a lot of consideration and extremely careful thoughts.
To begin with, leaving aside Xian Bao Bao whose mind was simple and innocent, Bai Zemin believed that he could trust everyone present; Shangguan Bing Xue, Wu Yijun, Xian Mei'er, Angelo, Eleanora... At this stage it could be said that the fates of all of them were tied to his in some way or another.