Eating cold food that's supposed to be hot?!
I asked chatgpt and basically it was easier to prevent being poisoned for various reasons (easier to inspect, more time for taste testers, etc.). Other reasons for eating cold food was that demanding hot food was considered undisciplined for a samurai, it was more practical during war time and cooking methods were limited at the time.
Apparently, real life Nobunaga still ate cold food just like any other Daimyo to avoid being poisoned unless he was absolutely sure he was safe.