Your answer lies in your photo. RH is function of how much water vapor the air at a specific temperature can hold. In your case, the sensors show a 10c temperature difference.
Here’s an over simplification of what that formula looks like. In short, a hotter environment can hold more moisture.
However, in the case of your circular hygrometer, it looks like the humidity sensor has failed. the 10% reading is indicative of a failed sensor. I recently found out why. These sensors have a coating on them. If they were mishandled(someone touched them during manufacturing) or somehow the chemical coating was worn off, they will stop reading accurately and eventually fail.
I had both the Creality Pi and Sunlu S2 in my office with the intent to determined which one I was going to keep. The Sunlu S2 failed in an epic way. One in particular was that both dryers did record RH very accurately. You can find that report in this link Sunlu S2 VS Creality Space PI Bake-Off Review
Here’s an example of what I mean. I took multiple sample readings inside the containers and the temp sensors were wildly off. The Creality was the least of the worse but Sunlu was laughable.
Sunlu clearly does not know how to design a dryer. I mean sure, force enough hot air over anything and it will dry, but as a piece of instrumentation? Well… let’s just say this, if they made cooking ovens and I was in competition for Baking, I wouldn’t trust what was on the dial. 
In a word, their products suck. The S2 was returned to Amazon.
What this shows you is that when you see a YouTuber try to sell you on the notion that this drier does the job, you’ll know their full of Sh*t and really didn’t test it properly. So now you can ask the question, what else are they wrong about?
The dead horse I will continue to beat; trust no one–not even me–verify everything for yourself. But make sure your testing methodology itself isn’t flawed. Drying a wet sponge like I see so many YouTubers do as a dryer test only shows that anything wet, heated enough will dry. However, what we really want to know is if the plastic inside is dry.
Here’s my dream dryer specs:
- The humidity and temp sensors should be inside the chamber not inside the electronics enclosure like all dryers today are. This will allow for “Truer” readings.
- There should be three sensors throughout the chamber and an average should be taken.
- The drier should have a scale baked into the mechanism to allow for weighing moisture. This is the only truly valid test of how much moisture was in the spool.
- The drier should have a USB interface with application software to log and record drying and allow one to maintain a database of filament weights and moisture.
- For a single spool, the drier should be under $70.
- It should be a square box, not this fancy sh*t that requires half a desk space to open the chamber but looks pretty.
- The display should be backlit and stay on.
- The touch screen should be solid capacitive outside the dryer container so one gets the same touch experience as one might on the a phone. “ALL” of these driers apparently are using the same Sh*tty Chinese maker for their touch displays and in my testing, it was clear that none of them worked well.