I can't read the original article because it's paywalled, but assuming that the original claim is correct ("increased performance by approximately .5 of a standard deviation across all tasks tested") and that by "significant" you mean "statistically significant" then you are spectacularly and confidently wrong.
Imagine we have a normal distribution of IQs around 100 with a standard deviation of 15.
Imagine there were some intervention which resulted in a uniform increase in IQ by half a standard deviation across the board. Perhaps the intervention is "literally add 7.5 points to every single score in the treatment group."
You seem to be asserting that because the effect size is "only" half a standard deviation, we have no way of determining whether or not the intervention actually increased scores, no matter how much data is collected. We could collect 100 million IQ scores in the control group, and 100 million IQ scores in the "treatment" group, and see that the average score in the control group is 100 and the average score in the treatment group is 107.5, and we'd have to say "nope, the null hypothesis looks completely plausible here, because the effect size was just half a standard deviation."
Does that seem like a reasonable claim?