immigration charging for tm30?

Today myself and my Thai spouse went to Buriram immigration to notify them that I was now living in his home.The officer told him that the fee for this service is 500 baht and that he was lucky that he didnt fine him for registering late.(we arrived in Thailand at 6pm on Saturday from Malaysia and stayed in Bangkok hotel 1 night) at the time we were at immigration I had been living in his house for approximately 15 hrs. When I explained this to him he only replied Mai pen rai
my spouse answered all of his questions such as when and where did you meet her? What work does she do and how much money does she have? Salary etc
I was under the impression that Thai people registering an alien in their home was free. Obviously not.
Has anyone else had the same experience?