"... CEO Jeff Bonforte (who joined the company only five months ago) says that Cselle simply decided that he was no longer happy at Xobni, and wanted to try building his own startup. ..."
and
"... I’ve wanted to be a founder of a company that makes a difference. I’ve wanted to build a workplace where people can be creative, productive, and happy, and a product that delights users and improves their lives. I feel like the time is now ..."
Reading the comment makes it pretty clear why he left. The number of first person references and self-promotional statements there suggest underlying personnel conflict.
Whether the company is going up or down at this point will probably depend on whether it's a development play or a marketing play. Whenever core engineers bail you usually end up with worse people doing a more incompetent job. Sometimes OK if the value is all in the marketing, and technology is getting in the way.
