What you might be missing from the story is that the customer was more likely than not using a landline to call technical support.

The ADSL filter sits between the telephone line from the street and the telephone.

Disconnecting the filter is the equivalent to yanking the telephone socket out the wall and if you do that during the call … no more call.

At this time many people were already using cordless phones and mobile phones were making inroads, so the link between the call dropping and removing the filter might not be immediately obvious to a clueless end user.

Source: I have had the misfortune of phoning telco helpdesk services where this kind activity would absolutely happen.