House-hacker forced to move before 1 year mark because of job

[Kelvin Lozano]

I'm listening to Brandon Turner's book "The Book in Rental Property Investing" where he mentions that a house hacker must live in the property for a minimum of 1 year in order to be able to "qualify".

What exactly does he mean by "qualify" and what happens if the investor/house-hacker moves before the 1-year mark? For me, the largest risk I foresee is job relocation.

Thanks,

Kelvin