Grilling may not be the best word there, but if you say you worked with language X, I think it makes sense to give you some questions about it to gauge how good you are with it. Some people stuff the resume by mentioning every language that they did for a toy project once in college, and then we don't want them to be put in charge of the project which requires deep knowledge of the same language. Better to find it out in advance. That doesn't necessary means that candidate will fail and not be hired - just maybe not for the project that requires the knowledge they don't have.