Hypothesis presented seems plausible.
I was surprised to learn Andromeda is twice the diameter of Milky Way. I would be curious to know the average spacing between the red group stars he spoke of, my off the top estimate would be .15ly.
Check out Alcyoneus( largest known galaxy)
I don't know what the spacing is however it is noteworthy that the predicted collision is expected to be fairly peaceful,more of a merger than something cataclysmic.
I still can't get over the Milky Way being a barred spiral.
I once went to a spiral bar.
I was pretty dizzy when I left.
Even starry eyed you could say