Game Analysis Blunder Question

Hello, I am wondering of someone can help me to understand why I was flagged as a blunder on move #9 as well as an inaccuracy when castling. My main issue is when I moved my rook to the open file it claims this is a blunder. I cannot understand how that can be. The computer claims that it is because I "eventually" lose the pawn. It seems absurd to me that that would constitute a blunder. I moved my rook to an open file on the side I did not intend to castle on. Upon further review, it seems that the computer viewed queenside castling as the appropriate side to castle. But I intentionally decided not to do that and from what I understand, it is up to the player to determine what style of game that that they want to play. Appreciate the feedback!! Thanks! [Site "Chess.com"] [Result "1-0"] 1. e4 Nf6 2. Nc3 e5 3. Nf3 Bc5 4. d4 Bxd4 5. Nxd4 exd4 6. Qxd4 Nc6 7. Qc4 Qe7 8. Bg5 O-O 9. Rd1 Qe5 10. Be3 d6 11. Be2 Bg4 12. f3 Bh5 13. O-O b5 14. Nxb5 Rab8 15. Qxc6 Rb6 16. Bxb6 axb6 17. Qxc7 Re8 18. Nxd6 Qe7 19. Qxb6 Nd7 20. Nf5 Nxb6 21. Nxe7+ Rxe7 22. Rd8+ Re8 23. Rxe8# 1-0

Your king was left vulnerable, it was better to accomplish the same task by castling long. Paul Morphy attacked in many ridiculous fashions, but never left his king exposed unless he calculated he'd checkmate first. So O-O-O was better, because it got the king to safety in time. Your opponent's queen was staring down the board and he could open it up. Castling to either side is not the player's choice whatsoever, it's about how the game shakes out independent of either side's overall desire.