That's not entirely true, the "threshold of originality" is relevant. Contributing typofixes or even things like minor non-functional refactorings (i.e. renamin

That's not entirely true, the "threshold of originality" is relevant. Contributing typofixes or even things like minor non-functional refactorings (i.e. renaming methods or variables) isn't going to qualify as an original contribution. A common mistake is thinking stuff like relicensing is some kind of binary 1-or-0 thing. It's not. It's a legal concern, not a technical one and is therefore subject to many messy human interpretations of ownership, law, et cetera. In any case it does not matter here because contributing to mold requires your changes to be available under both AGPLv3 and MIT, and so any derivative proprietary works can be considered derivatives of the MIT licensed version. It therefore isn't "changing the existing license", it's "making a proprietary derivative, which the existing license allows."