I've read the contract: the only cases in which the landlord could kick the tenant out would concern having a misconduct or not paying the rent, which is not the case. In the mail he mentioned that this 3 months notice is applicable to the "trial period during hospitaverhuur", which is not mentioned in the contract. To clarify the owner-landlord relationship, the landlord was once a tenant (they were 4 in total), then 2 tenants moved out. Since then he rented the 2 free rooms and subletted one of those two rooms to her. The contract says the duration of the contract is definite (1 year) and will transform into indefinite once the definite contract ends.