Are you being misled by the term "bitter lemon"? This is a popular British soft drink, originated by Schweppes, which appears to be similar to the lemon tonic mentioned in the recipe. I don't know how similar the two drinks are as I have never heard of lemon tonic until today.
I have a saved search that I use that should exclude non-alcoholic recipes. I also have a different saved search that only has non-alcoholic recipes and it doesn't show up there.