yes, he will accept the job offer if he is offered, but what if he is not offered? he has all the rights to secure himself. in such a case, he has to think only about his own situation. i am sorry but i dont think that it is unethical. because, in this case, he still has some chance of going to phd and he does not have to think about anyone else.
so, i think, you shouldn't judge him so harshly...