Some Android phones really have input lag, but it is not caused by CPU load. For example, on my phone, there is approximately 100-150 ms lag between tapping the screen and registering the touch. The lag is not caused by CPU load, but by slow touch sensor.

I don't think Apple has any smart code optimization tricks. Either they have a faster touch sensor or just some people believe that if something is made by Apple then it is of a better quality.

Here is a comparison of input lag in games in iOS and Android [1] and it shows similar results: 80 ms between a tap and reaction on screen.

[1] https://blog.gamebench.net/touch-latency-benchmarks-iphone-x...