That is for people with PCOS though!! If you are underweight any PCO tendencies you may have will be non-existent and at that point you need to do whatever it takes to keep weight on.
Sugar with a meal is fine for most people. An apple and mixed berries in yogurt is fine for everyone. Some sugar in coffee when you're already underweight is no big deal for the majority of everyone (exception those with severe PCOS, but you don't HAVE THAT.) You are worrying based on advice that was not even directed towards you.
The people who have issues with sugar are those with a lot of weight to spare and/or with moderate to severe PCOS. Several of those people were then insisting on following the standard diet (telling themselves it would be better for their sway) and having skim dairy, gummy worms, and very high carbs. That is not applicable to you - first of all because you didn't need that type of diet, and secondly because you're not eating that type of diet anyway.