I think what they're trying to say is zero calorie sweeteners can lead to weight gain. Artificial sweeteners have been used in the agriculture industry for quite some time as food additives to increase the weight of livestock.

Quoted from an animal feed ingredients producer and linked to their info: "The ultimate purpose of using sweeteners is to promote the animal’s continuous hunger, thereby increasing the total feed intake and improving the performance of animal production."

Artificial sweeteners themselves are usually zero calorie and don't directly add weight. Instead they cause a higher insulin release when you do eat something later. This can cause you to consume more simple carbs and more calories overall in order to feel satisfied.

https://pubmed.ncbi.nlm.nih.gov/27956737/

Edited to add sources and point out that we add zero calorie sweeteners to animal feed because the research is solid and we know the animals will gain more weight on them. There are no conflicts of interest. We want the animals to gain weight and the research supports using the sweeteners to accomplish that.