The list is titled “Top Feeders to Medical School”. The problem with such lists is the ranking implies that college name is a primary driver for medical school admissions. That’s not how medical school admission works. College name has little direct influence.
Instead I’d expect the largest contributing factor for the different percentages of alumni who attend medical school is different percentages of well qualified students who apply to medical school at different colleges. More selective colleges are more likely to have well qualified students than less selective colleges, who are more likely to be admitted if they choose to apply to med school. Some particular colleges also have a far larger portion of admitted students who are interested in attending medical school than others.
This is not to say that which college you attend makes no difference for medical school admission. There are many ways in which a college may influence chance of attending – offering BS + MD combination programs, having a greater degree of grade inflation or harsher grading than typical, weeding style approach vs more supportive, different advising, different degrees of committee screening med school applicants, differing distribution of students by state (in-state med school advantages), peer influence due to differing portion of peers who are pre-med, etc. However, such lists tell you little about whether such effects will have a net positive or net negative on a particular student’s chance of admission to med school.