I checked Manta website https://manta.network/ and X https://twitter.com/MantaNetwork but there is no information about the airdrop worth 500K USD. Everyone should be cautious and should not participate in this airdrop.

When I logged into the website provided by the OP, I received this message:
Dangerous site
Attackers on the site you're trying to visit might trick you into installing software or revealing things like your password, phone, or credit card number. Brave strongly recommends going back to safety.