Not sure about the node since I've never used it. However, I have used DHT22's in the past - they are not much better than the DHT11's and will occasionally give back a rubbish answer. As the
isValid flag is false, that suggests that the result was rubbish but that the node author decided to make the values zero in such a case - not a good choice in my opinion, they should be something obviously wrong like -99 or, even better,
By the way, the DHT 11/22 are rubbish because they are not only terribly inaccurate to begin with but also the sensor drifts over time.
I recently was putting together another sensor platform for the house and decided to put a DHT22 amd a SI7021/HTU21D on the same platform (ESP8266 based), here are the current readings (the DHT22 is the top reading):
As you can see, there is a very significant difference between them. When I tested this platform along-side some of my existing ones just to make sure that I didn't have a duff sensor, the SI7021 gave readings consistent with the other sensors which were either other SI7021's or BME280's.