Every license is a unique snowflake, but if you're going to stay sane and get on with your life you need some categories and lines. Redis is not available under a license that is open-source in any of the usual senses - not OSI-approved, not DFSG-compatible, not FSF-approved. That is a big deal. Matrix remains open source under a license that meets all those criteria. It's not a technical distinction, it's the line in the sand that stops open-source from being whittled away to nothing.