The guitar teacher's manager is probably and ex trumpet player who has NO idea that the techniques are different.
Finding a proper DB teacher is really difficult. Giving one enough work to make it worth their while getting out of bed is hard unless it involves teaching 'cello as well.
The guitar teacher is payed by the hour. "Can you teach bass? It will mean more hours." "Of course I can, when will I start?" Bass, how hard can it be? You know how that works.
Try and talk to the guitar teacher personally. She/he will probably be cool about it and might even welcome input.
There are elements of technique which are easily adaptable between violin and DB, especially if the teacher has had some training.