Astra in this sentence above is stating the name of the person that's doing the work i.e smiling and reading.
Noun as we all know can be a name of either a person, an animal, a place or anything at all. In the above sentence, it stands for a name of person. A person who is doing a work in a particular way(thoughtfully).
A noun can also be the subject or object of a verb. In the sentence above, it is serving as the subject of the verbs(smile and read).
Albus was put in Slytherin. The sorting didn't make a bad choice because maybe Albus could raise the Slytherin House liking considering everyone in the Harry Potter world be hating on them. So with a Potter in Slytherin it could help the house.
