Looking at the article you used for this claim, it is apparent that eating sweets such as ice cream does in fact not make you smarter. In the article a few paragraphs down it is stated that eating ice cream for breakfast is "a really bad idea. Research has shown that sugar is harmful in many ways. Ironically, in the long run it will increase your risk of depression, reduce your brain function, and make you more susceptible to Alzheimer's," wrote Rafi Letzter, a science graduate from Northwestern.
The claim proposed comes from a study by neuroscientists in London, who were not able to have a large sample size to confirm their information. In instances such as these, it's smart to look closely at the research, consider the organization that published the studies, and ask ourselves if it is reputable, seems to have highly qualified scientists on board, and whether it has a stake in the study's results. In this case the information could not be backed accurately by other sources therefore it is false.
Using a different source to fact-check this claim, GreenLight argues that "Traditional ice cream is high in sugar and fat, which can outweigh any potential benefits, no matter what time its consumed." This offers us a new prespective stating that ice cream and sweets will forever be bad for us, no matter what time we consume them. They are high in sugars and very low in things that can benefit us, like macros and protein.
This makes sense though, as we don't usually tend to eat ice cream when we are hungry or in need to become smarter, perchance. We do it because it tastes good and we enjoy it. We must leave it at that and admit that it isn't good for us, rather than trying to rationalize with ourselves that it's beneficial for us in order to avoid the guilt of consuming it.
https://greenlight.com/learning-center/parenting-and-family/ice-cream-for-breakfast