There is no functional difference between doing just an announcement and doing an announcement with a series of builds containing the patch while withholding the source code. You do understand that right?
This lets an AI agent look at the changes made from PHP 4 to PHP 5 and it also lets the agent guess what type of vulnerability it must be.
I mean an agent can walk those changes, but it's close to just walking all the whole source / research from scratch at that point.
At this point shipping the build already may have been the best option but not necessarily everyone is actually able to ship yet. And this is of course assuming the actual vulnerability is the same one as the PoCs that are being tried, and not something even nastier instead