Having a beer is not a no no in Dubai.
I have been there many times and you are able to drink in the hotels and bars, as long as you obey the rules and are not found drinking in public view outside of these areas there is no problem.
You also cannot be found to be under the influence in public.
If you obey the rules you are fine perhaps the said person may have had more to say at the time to the Security guard which I would say more than likely caused the problem.
People have to remember in a foreign country respect the laws.