Is my bf [26m] interested in this [30F]?

The other day i saw his message on insta to her that she was asking for a favour because this girl is his friend’s sister. She was asking if she can drop off cash to his brother.

After that he asked her to buy him food or like treat him because he did her a favour.
I asked him oh so its like a date. And he just said shes older 30+ and is like a sister.

He said i can come with them but he knows I’m not that type of person. And i guess he’s just saying stuff to reassure me. But why would he want her to treat him just because he did her a favour, which means he is interested?

Tldr: My bf’s friend’s sister asked him for a favour, now he asked her to treat him food.
Is he interested in her?