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.
BTW, Alexander’s army, after conquering Persia, was largely comprised of local mercenaries from those places.
Having maintained a deep desire to wet his feet in the “encircling ocean” that Alexander’s contemporaries believed to exist east of India, he could have simply used those newer, less homesick additions of his army to press on, but didn’t.