No License

Whenever there is no hardware or software license declared for a product, that means that the license is by default proprietary.

See https://choosealicense.com/no-permission/

Thus, when somebody claims that they are open source but does not document their license in writing, they are not legally open source. Such non-declaration is like an adhesion contract where the only option for the signatory is acceptance or rejection. As such, the proper response from the standpoint of open source collaboration is "Open Source or gitfo"