Your lemon curd is full of thickener (egg yolk) and sugar (honey) too.
What thickener did they use? Soy lecithin? That’s the same thickener as found in your egg yolks.
What sugar? Just regular sugar? That has a similar glycemic index as honey.
Concentrated lemon juice is just lemon juice without the water. Was there also water in the recipe?
Sounds like your stomach trouble was due to something else. I’m not saying the lemon curd you bought was good quality, but it probably wasn’t much different than what you make. And those scary ingredients are the same as the ones that you already use.