How much exactly did you win from PD? How large were your original deposit(s)? Are you using TOR/VPN?
any of this rly matter or necessary as long as if he didnt cheat or use any exploit?
Well if he did in some way cheat they might not be able to detect it right away. Hufflepuff was able to use an exploit that was undetected for a long time after he stopped playing under that name.
Still not a valid reason to ask for so much info or holding his coins without explaining why.