"Mia avino falis en sia domo."
Translation:My grandmother fell in her house.
How callous of you not to ask about the poor lady's well being :) She is ONE person, and she deserves to go wherever she pleases outside of her retirement home on the Family skill!
Seriously now, I have no idea - there are a few sentences here and there that are not entirely related to the overarching theme of the skill, but that's probably just to make sure that people don't get too immersed on just one topic... or it could just be a mistake, you're gonna have to ask the course creators that.
In the notes section (it isn't available on the mobile version though), there is a small section mentioning grammar:
''' Tips and notes
THE PAST TENSE -IS ENDING.
For the past tense, use -is: La arbo falas. The tree is falling. La arbo falis. The tree fell. '''