I'm going to ask my neighbor to move the piano they play for hours a day away from the wall we share in connected housing
That sounds like a lot of work. Do you dislike your neighbors for their behaviors?
It is not true that I do not like my neighbors very much.
Asking your neighbor to decrease the noise volume is totally acceptable. Neighbors should be considerate about each others noise level.
It's my fault to make the wrong assessment of my neighbors.
It's all right, we all make mistakes and as long as you make it up to them that's fine! You might even find yourself befriending them over this matter!