That doesn't stop someone from lying about it, but it's not a casual claim, and doing so would probably bring community censure (as well as being easily falsifiable after time).

Security research is not always the most ethical branch of computer science, to say it mildly. Those are the people selling exploits to oppressive regimes, allowing companies to sit on "responsibly reported" bugs for years while hand-wringing about "that wasn't in the attacker model, sorry our 'secure whatever' we sold is practically useless". Of course the overall community isn't like that, but the bad apples spoil the bunch. And the aforementioned unethical behaviour even seems widely accepted.