It only becomes remotely intelligible if you include these extra constraints:

- Assume all other houses in the area also appreciated the same amount as the poster's house (say 2x).

- Assume the poster will only consider a move within the same area.

Now if they want to make a "lateral" move, they are looking at $2m houses, not $1m houses, since all other houses they would consider - local to their area - also increased in value.

I feel like they should just get a $1m house (yes, a "downgrade") if that's the case and have fun with their near-$1m profits, but what do I know.