I think he means smart as in "how long your model prediction takes". If your neural net (haven't actually met anyone who uses these in trading) takes 5ms to make a prediction that'll lock you out of a whole lot of trading opportunities/strategies.

Speed always matters, no matter where on the smartness spectrum you are, but it's relative. If your model prediction takes 5ms you're not getting much ROI out of investing $1M into shaving off 50ns in your data processing. But if your end-to-end latency without prediction is 1ms, you better invest in getting that down.