There are 2 different spirits in the picture.
The text "A change in perspective"
Do they see the spirits differently?! Why? Rom sees them the same way as Miko though? Is the guy's spiritual awareness faulty?
There's a whole chapter where Seto explains that Spirits are anomalies in reality and that they don't have a "canon" appearance. Everyone perceives them differently.
Romm saw the "middle-aged man" as something utterly horrible.
Mieruko saw it has the "middle-aged man".
In this chapter, the twist at the end is that the spirit that was following Mieruko's mom around is the "middle-aged man" as perceived by Mieruko's father.
Another example would be Mieruko's classmate who can only see outlines, her "spiritual awareness" is not faulty, that's just the way she sees them.
My best bet is that Mieruko's dad made that thing target him on purpose so that it would stop following Mieruko's mother, when he died the thing started haunting Mieruko. Whatever it is we know it is extremely powerful, and just like every other spirit so far it refuses to enter Mieruko's household, probably because of dad and François.