Hi,
The computer engine evaluates the game position by position. Based on its calculations, it believes that exd5 is a better move for you, therefore it considers Nxd5 a mistake. I couldn't find the line where you could capture his Queen, but most likely you're able to do this because he also made a mistake after Nxd5 (Bxe4 was his mistake). Also, just because you're able to take his Queen, that doesn't immediately justify Nxd5 (because who knows, maybe another move like exd5 could've let to mate, for example), so in a situation like that, even a move that wins a Queen would be considered a mistake.
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Hi guys. First time posting here. I noticed from my this game at 9. Nxd5, the analysis shows that its a mistake. However, when I asked it to elaborate, it shows me that I have lines that I can take the Queen. This is really weird. Can someone help to look into it?