I did have that personal information at the time. I was exposed to a lot of their personal information as I was helping them. I don’t exactly know what happened with Ohtani and Ippei, but if their relationship was somewhat close to mine, I could see how it could happen.
Interpreters are close with there players and often have access to personal information. With how close Ohtani and Ippei were it might be far to assume Ippei had access to this information. This isn't concrete proof backing Ohtani's story but does to speak to how it could be true.