Isnt "a la maison" the same meaning as "at home" in English?
It means both. "Une maison" is "a house" but since we don"t really have a word for "home" (except maybe "chez soi"), we use "la maison".
Yes. that's nice to know, but in this particular case what is the probability by your estimation that they don't speak about being at home but speak about just not being outdoor (en plein air).
The first hint on hover for 'il s'ennuie' is 'he feels bored', yet 'he always feels bored when he is at the house' is not accepted. Reported (1 July 2021).
Why is "...at home" rejected?
It's accepted now 23 Nov 2021