Congratulations... You're the first to even acknowledge the distinction :~D
Let me admit something. I'm not sure Matt and Trey, who wrote it, nor most non-Catholics in this country, know when or what the "Feast of the Immaculate Conception" is. Maybe they do, but I don't. It might just be lucky chance that it aired then.
This is not all that different than defiling a Nativity in a Christmas episode.
Rut Roh...
Whew! that's a relief. I thought it was just me.