Nah, it is not just an opinion. Security through obscurity is a capital sin in computer security design.
But I don’t think it applies here, it is not about security as @tonbi said, it is about keeping a competitive advantage until they are mature enough to release.
They don’t even have a brand yet, so it makes sense.
MaidSafe was also close sourced until a few years later after the ICO, this used to be a common point of criticism and misunderstanding back in 2014/15.