I believe the temperatures within the chart are "feels like" temperatures rather than absolute temperatures. The X axis shows absolute values (what would likely show on the thermostat).
At OPs original temperature (91°F) the danger zone would be around 60-70% and higher. At OPs last updated temperature (94°F), the danger zone would be 55% or higher.
I guess dry heat is a thing. I can do >110 fine, I don't like it, but I don't feel in danger. But its 10% or less humidity. Its usually better to wear more clothes just to keep the direct sun off you. Somehow wearing a hoodie in the desert in summer is comfortable. Its also nice not getting sweaty because it immediately evaporates.
I spent a summer in south India a few years ago during monsoon season. I was fucking miserable in my jeans and shirts until I switched over to wearing loose, flowing clothes made of bleached kahdi (loose homespun cotton) like the locals. It keeps the sun off you and even when it gets soaked it doesn't cling to your skin, and then whenever the rain stops it dries completely very quickly. Other westerners I met made fun of me for pretending to go native, but they had no clue how effective it was.