Besides, as noted in the post, this particular journal charges a fee for publishing.
This journal sounds like it is about equivalent to "self published" books, where you pay the publisher to print your book.
Journals are a business. The money to run that business has to come from some place, and it's a zero-sum game between authors and readers. The short-sighted open access proponents (not all are short-sighted, but many are) think that the words "open access" mean "free of cost to anyone involved". Not true. Open access journals shift the burden of funding their operation from the readership (such as with the traditional subscription model, regrettably known derisively as closed access) to the authors. Instead of being free to publish (which means that *anyone* can publish), open access means only those able to afford publication can get their results disseminated.
Open access means the author pays. That's it. Nothing more.
In particular, it says nothing else about the quality of the journal. While the quality of the journal in question here may be highly suspect, and while a lowest-tier journal might not be able to survive in other than with a a business model that includes payment from authors, being open access is orthogonal to quality. Even the highest tier journals have options for the authors to pay for open access, but, repating for emphasis, the authors must pay for it.