how was this a brilliant

[Event "Live Chess"]
[Site "Chess.com"]
[Date ""]
[Round "?"]
[White "Joe_mamd1"]
[Black "IlyasAth"]
[Result "0-1"]
[TimeControl "180"]
[WhiteElo "309"]
[BlackElo "306"]
[Termination "IlyasAth won on time"]
[Link "https://www.chess.com/game/166516227884"]

1. e4 e5 2. Nc3 Nf6 3. Bc4 Nc6 4. d3 d5 5. Bxd5 Nxd5 6. exd5 Ne7 7. Nf3 Nxd5 8.
Nxd5 Qxd5 9. O-O e4 10. Ne1 exd3 11. Qxd3 c6 12. Bf4 Bc5 13. c4 Qd4 14. Rd1 O-O
15. Qxd4 Bxd4 16. Rxd4 Re8 17. Nf3 b5 18. c5 Rb8 19. Bxb8 a5 20. Bc7 a4 21. Re1
Rf8 22. Red1 Bg4 23. Rd8 b4 24. Rxf8+ Kxf8 25. Rd8+ Ke7 26. Rd6 a3 27. b3 Be6
28. Nd4 g6 29. Nxc6+ Kf6 30. Nxb4 g5 31. Bd8+ Ke5 32. Bf6+ Kxf6 33. c6 h5 34. c7
Ke7 35. Rc6 Kd7 36. c8=Q+ Ke7 37. Qc7+ Kf6 38. Nd5+ Kf5 39. Rxe6 fxe6 40. Ne3+
Kf6 41. Qe5+ Kxe5 42. g3 Kd6 43. f4 Kc5 44. fxg5 Kb4 45. g6 Kc3 46. g7 Kb2 47.
Nd1+ Kxa2 48. g8=Q Kxb3 49. Qxe6+ Ka4 50. Nc3+ Kb4 51. Qc6 a2 52. Qg2 a1=Q+ 53.
Kf2 Qxc3 54. Qf3 Qc5+ 0-1 

I was wondering how the rook's move was brilliant? It didn't seem to sacrifice anything, but I might just be as blind as a bat, thanks in advance!

It’s because you left a bishop hanging. The queen could’ve taken the bishop, but if she did, it was mate in one.

[White "Joe_mamd1"]
[Link "https://www.chess.com/game/166516227884"]
[Date ""]
[Event "Live Chess"]
[BlackElo "306"]
[Round "?"]
[Site "Chess.com"]
[TimeControl "180"]
[Termination "IlyasAth won on time"]
[Black "IlyasAth"]
[Result "0-1"]
[WhiteElo "309"]

1. e4 e5 2. Nc3 Nf6 3. Bc4 Nc6 4. d3 d5 5. Bxd5 Nxd5 6. exd5 Ne7 7. Nf3 Nxd5 8. Nxd5 Qxd5 9. O-O e4 10. Ne1 exd3 11. Qxd3 c6 12. Bf4 Bc5 13. c4 Qd4 14. Rd1 14... O-O (14... Qxf4 15. Qd8# ) 15. Qxd4 Bxd4 16. Rxd4 Re8 17. Nf3 b5 18. c5 Rb8 19. Bxb8 a5 20. Bc7 a4 21. Re1 Rf8 22. Red1 Bg4 23. Rd8 b4 24. Rxf8+ Kxf8 25. Rd8+ Ke7 26. Rd6 a3 27. b3 Be6 28. Nd4 g6 29. Nxc6+ Kf6 30. Nxb4 g5 31. Bd8+ Ke5 32. Bf6+ Kxf6 33. c6 h5 34. c7 Ke7 35. Rc6 Kd7 36. c8=Q+ Ke7 37. Qc7+ Kf6 38. Nd5+ Kf5 39. Rxe6 fxe6 40. Ne3+ Kf6 41. Qe5+ Kxe5 42. g3 Kd6 43. f4 Kc5 44. fxg5 Kb4 45. g6 Kc3 46. g7 Kb2 47. Nd1+ Kxa2 48. g8=Q Kxb3 49. Qxe6+ Ka4 50. Nc3+ Kb4 51. Qc6 a2 52. Qg2 a1=Q+ 53. Kf2 Qxc3 54. Qf3 Qc5+ {0-1}

I added the sequence above

What it designates as brilliant depends on your rating. Of course it isn't very brilliant to leave a piece hanging to get a mate in 1. Their idea is that it encourages you but patronises might be another word.

chess.com doesn't really know