He has 50+ peer reviewed studies so I think he's aware that correlation does not equal causation. https://scholar.google.com/citations?hl=en&user=iOqYqV4AAAAJHow have schools in other countries that also have laptops done education-wise? without a proper comparison this is meaningless. Correlation does not equal causation.
This is an article based on an article based on his testimony to congress. Blame journalism not the research for the lack of details.
There's even a direct quote that this is not anti-tech. It's about using tech better:
"This is not a debate about rejecting technology," Horvath wrote in his testimony. "It is a question of aligning educational tools with how human learning actually works. Evidence indicates that indiscriminate digital expansion has weakened learning environments rather than strengthened them."