Why is White's accuracy 99.7% instead of 100.0%? Here is a short game played online at chess.com.
[FEN &quot;&quot;]

1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. c3 d6 5. d4 Bb6 6. dxe5 

Black resigned for some unknown reason; maybe a mouse slip or he/she needs to leave. When the game was analysed at chess.com, the game accuracy of white is 99.7%. In my humble opinion, every White move is accurate (unless one considers 3. Bb5 to be more accurate than 3. Bc4). But why is the game accuracy for white is not 100%? What is the 0.3% that White l missed?
Probably, as you pointed out, Bb5 instead of Bc4.
The Ruy Lopez is considered very very marginally better/more critical than the Italian by humans, so it'd make sense that the engine used here'd agree.
Certainly, however, the Italian is fine, and the difference is very marginal.