At 42% humidity, I’m guessing they live in a subtropical climate. Florida’s?
https://www.weather.gov/lsx/monthTab
It was in the upper 80s/lower 90s throughout July and August, when this data was likely collected. And relative humidity hit 80-90% every morning, averaging about 65% as it warmed up. It's sticky in summer. I live in Michigan, and even with a cool breeze from our magnificent freshwater lake, half an hour inland it's similarly hot and humid. I kept our house at 78 when we're home, 82 when it's just the dog, and 76 when company comes over. I think the air conditioner keeps humidity in the 40% range, though I'm reading this article because I lack a hygrometer/air quality sensor and don't really have hard numbers for that, only that humidity is significantly less indoors than out.
Also, he mentions that the orientation of the case causes convection off the ESP8266 to increase the air temperature by a couple degrees (Farenheit).
If you're one of the Silicon Valley HN readers looking to move to the wide open spaces and relaxed culture of the Midwest, do be aware that climate is a big deal; coastal California's perpetual mild climate is an aberration.
March spring hits and the pollen is crazy until June and by then it's too hot to really be outside without tree cover from 9am-8pm until around now.
My area is one of the worst pollen places in the country. You owe it to yourself before moving to look at a pollen map as well.
Since air holds more water at higher temps (and a lot more, 90F air can hold almost 3x as much as 60F air), just comparing humidities without considering temp doesn't say much.