Iirc he was in Japan for 3 years total, and only spent 18 months of that under Nobunaga. Not only is there a zero percent chance Yasuke was an actual samurai (for fucks sake they didn't even bother to write down the guys actual name, "Yasuke" was just his japanese nickname), there's a zero percent chance he could even read or speak Japanese beyond basic "go here, hold this" commands.
Illiterate foreigners that can do nothing but lift heavy shit and scare people are not elevated into upper caste status in less than a year.
Even the guy who the Shogun TV show was based on, William Adams (who was a REAL, DOCCUMENTED FOREIGN SAMURAI, title and everything) offered valuable military intel and strategies to his new Lord, along with aiding in the construction of new western weapons and ships, which is why he was given the title and status. He also lived in Japan for the rest of his life and still has decedents there to this day, unlike Legendary Samurai Yasuke who vanished and was never heard from again.