What's the right way to deal with gaps in the prayer row?

Assalamu alaikum, everyone. I went to pray Isha with my father at our local musalla. I got there a little before him and went to the second-to-last row. There was an elderly brother in a chair against the wall on the left, and a younger brother further right, but he started his prayer more toward the middle of the row. The older brother gestured for me to fill the gap between them, but the space was pretty big and I couldn't close it all the way- maybe a small child could've fit between me and the person on my right. I thought the younger brother would shift over, but he stayed put the whole prayer. The row filled up, so my father ended up behind me. After salah, he asked why I left that gap. I explained that I stood naturally next to the elderly brother since he couldn't move during prayer if I squeezed over. My father wasn't happy; he said I should have at least widened my stance to make the gap smaller, because gaps are where shaitan stands. I've heard in lectures that the hadith about gaps in prayer isn't about physical space but about things like arrogance or bad feelings between people causing the gap. I told my father that, and said I didn't do anything wrong since I had no ill will toward anyone. But then he said we never accept what he says and always argue and can't admit when we're wrong. I've left it at that, but I'm still wondering: what should I have done? Move to the middle of the gap? Widen my legs? Or just stand as I did? JazakAllah khair for any advice.