Yes, "open source" is not a protected term, nor a trademarked term, so anyone can call anything "open source".
However for lots of people who deal with software, calling this "open source" is highly misleading and at worst disingenuous. Within the open source software (and wider software world), it's quite clear and non-subjective whether software is open source. There are numerous, nearly entirely harmonious definitions of "open source". Under those rules, within that community, this is not "open source".
However for lots of people who deal with software, calling this "open source" is highly misleading and at worst disingenuous. Within the open source software (and wider software world), it's quite clear and non-subjective whether software is open source. There are numerous, nearly entirely harmonious definitions of "open source". Under those rules, within that community, this is not "open source".