Gst rate on room rent and food

Few days back, I stayed in a resort wherein my room tarif was around INR 5000 and food which was eaten was around 1200 per day per person. GST levid on aforementioned rates was 18%.

My question is:

1) As per my limited understanding, GST should have been 5% on food and room rent both. However, explainination given to my by reception staff was that since resort has room rents going upto INR 12000, hence GST is 18% on "ALL" room rent and food as well.

Could someone please help me?