According to the HereLink manual. It uses 2.4ghz frequency for wireless communication and claims video streaming in 1080p up to 20km range. How is this possible? If it can transmit up to 20km then it shouldn't be wifi right?
Wi-Fi and 2.4GHz are not necessarily the same thing.
2.4GHz is part of the ISM band (Industrial, Scientific, Medical) of frequencies that can be used for short range communications.
Wi-Fi is a protocol that commonly uses the 2.4GHz spectrum. However 5GHz and 6GHz have been added recently. This protocol is also known as IEEE 802.11 and the term "Wi-Fi" is actually a trademark of the WiFi Alliance.
Another protocol, LTE (Long Term Evolution) was developed for cell phones. I believe the Herelink is using LTE and not Wi-Fi on the 2.4GHz spectrum.