I think most of that conversation was referencing their two "feeder schools", which are affiliated with the high school. If I recall, the poster said most kids that show up have played football at various pop warner programs, etc.
Which I guess begs the question, what constitutes a "feeder" program? IMO, it's one that directs the majority of kids to a HS and has some level of communications or strategic continuity with the HS.
If the St. Cajetan's football team is sending players to Mt Carmel, St. Rita, Marist, Brother Rice, and St. Laurence and running an offense completely independent of all 5, I don't really think it's a feeder for any.
On the flip side, if 90% of the Park Ridge Falcons players are attending Maine South and the higher age group teams are running schemes loosely based on Inserra, it's a feeder, to Maine South. It is NOT a feeder to Notre Dame, even if a few guys attend.