I don't think that's true for anything with a permissive license, only contributions to copyleft licenses. If I contribute code to something under the GPL then my contribution can only ever be distributed under something that is compatible with the terms of the GPL, the company cannot restrict those rights further in a new license without my consent to relicense.
If I contribute to something with a permissive license then it doesn't prevent the company from releasing new versions of the project under the BSL. The only restrictions on the permissive license is the copyright notices have to be included.
Their CLA faq talks about how its purpose is to allow them to release the software commercially. No other entity has that ability unless they ask everyone to sign a CLA of their own.
If I contribute to something with a permissive license then it doesn't prevent the company from releasing new versions of the project under the BSL. The only restrictions on the permissive license is the copyright notices have to be included.