HMO = Income from Property or self employment

I am looking for some feedback on a response I have had from HMRC. A friend has a large house and they have 3 lodgers, which makes them a HMO.
They need and want to declare the income to HMRC and I would say it should be declared under income from property, but HMRC have said it should be treated as business income.

This doesnt seem right, its their own home and I have always thought lodgers rent is income from property.

Has anyone else come across this or did I just find a tax officer who was confused.

thanks
Helenka2020