It's called 'hiding in plain sight' but you already knew that.
No, it's called "people calling something "secret" simply because they personally were ignorant of it."
The amount of public information on our cooperation with Ukraine in some of those labs is voluminous. It wasn't a secret. Here is a damn 2007 article in which we publicly announced helping Ukraine with labs to address Russian biological weapons and other biological threats. And there is plenty of stuff all through the intervening years. How else do you suppose the Russians knew to bring up those labs in the first place??
https://www.armscontrol.org/act/2005-10/threat-reduction-program-extends-reach-ukrainian-biological-facilities