He didn't do that. He pointed out issues with the cql syntax and specifically scylla's implementation of it. he is also uniquely qualified to make such a statement, as his Jepsen Reports are high quality analyses looking at various databases.
But to address your other claim: they solve the same problem of providing data to your application. They should be compared if that's the decision you have to make.
It's not 'fair' to compare CQL to SQL, if you compare CQL to DynamoDB's http api, which scylla implements as well, you'll see that cql is better: https://www.scylladb.com/2020/05/12/comparing-cql-and-the-dy...