How are game shapes determined?

This game was categorized as Sudden, saying that it was close but was lost by a mistake. How was it close and lost by a mistake when white's advantage had been consistently growing from the start? There weren't even any big mistakes from black! The biggest mistake was 1.3 behind the best move. It was white +1.9, and after black's worst move, it was white +3.2. Even if black had made the best move, white still would've won as its advantage had been gradually but consistently growing from the time the opening came to an end. Perhaps this game shape was chosen because the game was more like this shape than any other, but still, it does not describe it accurately.