Sometimes, there are sentences on Duo that don't seem to make sense, or don't seem that useful. The point is, that sometimes sentences don't need to sound perfectly sensible. Some them were just created to display a certain sentence structure, so that the learners can actually change or modify it accordingly, and use it on a different occasion.
Does 'the mother' sound a bit weird instead of 'my mother' in this sentence? Maybe. Is that problematic? Not really. There is no serious context issue.
Plus, I think it's not impossible that someone could be talkng about someone else's mother, and not theirs. ^.^