Unless they built their server with nand gates, I don't see running nginx reverse proxy to be incoherent with their philosophy.
The philosophy "Don't reinvent the wheel" however, is definitely inconsistent with their philosophy. They will reinvent the wheel whenever they feel they can make a better one. Just because they haven't reinvented every wheel does not mean "don't reinvent the wheel" applies to this group.
They chose to create the best solution they think they can. They don't seem to care whether or not that involves reinventing wheels. The original argument that they should seems pretty silly.