Seems like it was at most mid 70s around 9am
If you’re not used to the heat, it can be hard on you. Humidity makes sweating less efficient.
Marathoners need to drink a lot of fluid in the best of temperatures. Yesterday they needed extra.
Dehydration causes all sorts of symptoms including heart issues which apparently killed the runner.
There are also a lot of people who enter these things without being in great shape. At least that’s my observation from being in the occasional hospital tent (with a friend).