I think it's reasonable to assume that it belongs wholy to Uber and that he was acting illegally to publish it on github. He even showed us the sofa in the Uber

I think it's reasonable to assume that it belongs wholy to Uber and that he was acting illegally to publish it on github. He even showed us the sofa in the Uber office where he wrote it. He told us his manager asked him to write the code and seemingly had no idea that he'd written a database engine. He told us that they were paranoid of industrial espionage at the time. There seems to be zero reason to suspect that Uber carved out a specific exception to the usual employment contract enabling him to work on and release this code as FOSS while at the company.