The scenario allowed in your reference is not the same. The original scenario was a rental/income property declare principle (for some short period of time) for the purpose of shielding capital gains whereas the exemption you reference is a principle residence allowed to be used for rental/income. Note that you cannot declare another property as principle while you're renting out your homebase. I expect it is meant for cases where you might take a job transfer for a period of time.

The taxman never leaves money on the table.