Why did Bitcoin Core wallet send my coins to this address?
The transaction that shows up as confirmed (8f1fb5fa1) was confirmed almost a year ago in block 345970, although your client is showing it with a recent date. I think you might have not synchronized with the network before attempting to transfer the coins to your new wallet, at which point the client still showed the coins in your balance. You later caught up with the blockchain and your wallet noticed that the coins were no longer available, marking your new transaction as a conflict/doublespend.

If this is indeed the case, then this is perfectly normal. If this were your address then the wallet would notice this automatically and credit you with the coins. It could either be that you migrated your funds at some point to a new wallet or that malware was involved.