@Mohini6 Good luck with your project.
My first question to you: Does the basement have egress windows and doors? No windows large enough to escape in the case of an emergency would render your basement an illegal bedroom rental in my location.
In answer to your question about your STR regulation, it reads to me that if the basement apartment is separate in its entirety from the main house, only a person living in that apartment can sublease a room to a transient guest.
I would ask your agency further -- for example, if the basement apartment has a door that is accessible to the house above that is used as an emergency egress door or is the means of accessing the apartment by the occupants, i.e., they can enter your house via a foyer and then go through a door to the basement without using the other basement entrance, can you live upstairs and rent the basement as an STR. Best wishes.