You see this all the time with Mysql and Postgresql benchmarks. Typically when I see the two compared it is by someone with a decade of experience with one of the systems, and none with the other one. They use a workload that is optimized for their usual system. They also don't have a clue how to create a high performance version for the competitor, nor do they know how to configure it.
It's also true that the testers usually don't configure all the products equivalently. It's usually not (only) incompetence, they are pushing an agenda for their product or consulting services.