It not being recognized as an official OSI license does not make it "closed source", their source code is still fully and freely available to customers who can continue to using and customizing their own modified versions as they see fit. None of which they could do if it was "closed source".
Their software also converts into Apache-2.0 after their conversion period, where it by definition also becomes available under a permissive OSI approved license.
Which is both clearly spelled out in the article and irrelevant to my original comment where "Nothing about this announcement makes it closed-source software."
Being licensed under an OSI approved license (that their software converts to after their conversion period) makes it "Open Source" by definition, it does not make it "closed source".
Their software also converts into Apache-2.0 after their conversion period, where it by definition also becomes available under a permissive OSI approved license.