Press release came via email from SCEE with a PDF in it. I just copied the first passage and I can't make the rest or the PDF public. Sorry. But I guess every registred press outlet in Germany recieved that release yesterday. It's legit.
But we don't know. Your statement makes sense - but it's also possible that PS4 was at 999k at that time and Sony knew they would reach 1 million that week (or that specific day), regardless if GFK data was in or not. Or they calculated it back.
The press release comes also a little late, if Sony would be raving about shipment numbers, they could have released the PR back then when they shipped the million.