It would seem strange if they failed you just based on verbal information, especially seeing as getting drunk once 4 months ago is in itself not indicative of problem drinking.
There are blood tests that can be taken to see if there is any biochemical suggestion of excess alcohol consumption over time. If, as you say, you don't drink more than small to moderate amounts, these tests will likely be negative and there will then be even more evidence supporting the fact that you do not drink too much and thus, should not be considered unfit to hold a class 1 certificate.