Tallinn's actions back up his explanation: in 2009, before he invested in any AI lab, he donated substantially to the nonprofit Singularity Institute for Artificial Intelligence, which was later renamed the Machine Intelligence Research Institute (i.e., Yudkowsky's outfit).
Some of us (certainly Yudkowsky and Habryka, the leader of Lightcone Infrastructure, which runs Lesswrong) wish people would stop believing that they can improve the bad situation caused by AI research and development by investing in (or working for) frontier AI labs, but that is what the preponderance of the evidence shows Tallinn (and Dustin Moskovitz and others) did sincerely believe.