The paper is an analysis performed on a larger dataset. No one created or ran a 15 year study on egg consumption. Someone ran a 15 year study that included dietary survey questions that happened to include eggs, and then someone other group mined the dataset for this analysis.

This particular study (AHS-2) was initially funded by the NIH (and has continued with NIH and mixed funding): https://publichealth.llu.edu/adventist-health-studies/videos...