Lex became extremely sensitive towards the intentions of others. More important than just intentions, he became exceptionally skilled at determining who was acting on those intentions - only as long as he was the intended target.
His instincts rose to a whole new level, so that if anyone within a radius of 100 miles of him did anything at all, with him as the intended target, whether it was good or bad, he would be able to sense it.
Perhaps what Dao Lords possessed was a much more powerful version of this ability. He was still not certain how it worked, besides that his instincts were responsible for it.
As a result, anyone and everyone within a hundred miles of him who was observing him with the intentions to harm him, or take advantage of his weakness, were teleported over.
By the time this happened, an entire one second had passed since Lex had broken his seal.