I have no idea. I found out after getting to grad school that I had far less relevant experience than most of my cohort. I think there are not a lot of people who want to work on my particular (fairly obscure) niche, and that my advisor may have lobbied for me for that reason, although I also have reasons to think that may not have been true. I also think that my GRE scores were higher than average, and that probably helped to make up for the lack of relevant coursework.