I too wondered about the distance from Western India to Nepal but have seen that reference more than once so I guess it is correct.
I think you underestimate Alexander’s victory over Porus. It was hard fought but a complete victory for Alexander.
I also think the reason for Alexander’s men wanting to go home was far more about years and miles from home and family than any fear of India’s soldiers but that is just my opinion.
Interesting stuff to research about, later!