That's good to know that this does not occur that often.
The thing that triggered me to ask is because my mom traveled back to Europe from her trip to Asia and she was wearing her Cartier watch and was held at customs. she also has lots of LV luggage, perhaps they thought it was fake. Anyhow, they researched the authenticity and also asked where she bought the Cartier watch, because otherwise she would have to pay VAT (tax) for the watch. Luckily her watch was engraved so they let her pass.
Silly right?
not sure where in asia your mother visited, but maybe because asia has a lot of knockoffs and a lot of people travel there to buy. so maybe seeing your mother with a lot of designer items, it just triggered a red flag for them.

or i could be wrong.