While Lex was observing the sealed domain, and discussing its possibilities with Pel, back in the Midnight Inn, the two Rhinocentaurs were giving their daily news. Lex had already informed Velma about the details of their agreement, and informed her to record everything they said.
Whenever he returned from his various tasks, he would take his time to check the veracity of the news they submitted, mostly by reading their soul language as he asked them about each piece of news.
The reason he told Velma about it was because since she ran the Midnight newsletters, he thought she'd find it interesting, and could maybe add it to the newsletter if the information was relevant or interesting.