Again - a considerable amount of research you put into this post, Jackie. Amazing!!
So this Thomas is also missing (either died or moved away) in 1900. He could have immigrated.
You originally found him listed as born in Horten, but tracing him back to his birth, it appears he is more likely the Thomas born in Borre.
The name Wilhelmine occurs in this family - that is worth noting.
The mother of this Thomas is Anne. We remember that the mother of Thomas was named in his death certificate as Anne (Anne Mahoney /Moroney/ hard to read). We are probably correct that this name is a mistake, and the respondent is naming Thomas's wife's mother.
It is just possible, however, that the confusion began because both mothers were Anne.
Obviously we have no proof of that hypothesis, I am only speculating.