Yes- a child can have a shortened frenulum and still extend their tongue past their lips. I wouldn't assume that your son is refusing to speak just because he's able to extend his tongue. If he isn't speaking at all, though, I would check with the pediatrician.
For anyone else reading, in case they don't know, "tongue tied" just means that the frenulum (the skin connecting your tongue to the bottom of your mouth) is shortened, so how severe the condition is would depend upon how short the frenulum is, case by case.
My son has a shortened frenulum and the only impact the condition has had was to inhibit his ability to breast feed- he could only do so with difficulty and would become so frustrated that he then couldn't do it at all. We were told that in some cases the situation is more severe and can impact speech development. In those cases there are procedures that can be performed to correct the problem.
I would consult with your pediatrician- they should be able to do an assessment and talk to you about what, if anything, needs to be done for your son.