So for Bitcoin holders one must give their private wallet keys to AChain? Or am I reading this wrong?

This is a scam coin, forget about it
You need to read whole announcement...
Bitcoin Wallet users need to import his or her own BTC private key to receive ABTC. ABTC System will not store the users private key, and performs encryption during the transmission. But just in case, please transfer the BTC on the private key to another address before you receive ABTC.
The ACT Wallet (including PC Wallet and Kcash Wallet) users will automatically receive ABTC without any further operation.
If your ACT or BTC stores in Huobi, OKEX, Ourdax and Kucoin, please wait for the receipt scheme to be issued by the exchange.
In principle they are not trying to stole your BTC... it is true that there is a possibility they stole previous BTC forks with this private keys... it your choice to trust them or not
