Sounds like he got in the tub first, then turned the water on. But hot water is not instantaneous. As the temp of the water goes up, you adjust the temp to your liking. If it gets too hot, get out of the tub.
I never get into a shower or tub and turn the water on, especially in a strange, new location.
Maybe this 76 year old had the IQ of a turnip. Or maybe he is physically disabled.
What a weird story.
Yeah, it sounds as if he must have been suffering from dementia if he forgot to adjust the water before entering the shower.
That being written, 150F is too hot for a residential application.
A decent motel or nice house should have a hot water circulator that keeps the hot water right at there all the time.