This also covers adult children playing games all day, or a variety of other situations. Seems weird to single out work from home.
Keep in mind this is a 1 bedroom ADA and so they’re probably targeting a specific type of tenant.
Their own logic seems to be - the rent covers all utilities (they have assumed a certain cost for utility based on some logic that assumes the tenant not being at home majority of the time; they're then saying - if you're going to spend more time at home, we assume you're going to go over our utility estimate).
Also, it's a 1 bedroom and they have a target renter in mind. Maybe they aren't expecting (planning) to rent to elderly folks or disabled people; Maybe their target is a working professional.