It's not that crazy. As noted by xliioper it's just a way for DL to alter the fare without refiling or being subject to corporate discounts. For all intents and purposes it's the same as the base fare and you earn MQDs based on both the base fare and the YR (which further points to DL viewing them as one and the same for all practical purposes).

The $2300 for a J fare is pretty low so not sure I would care that much how they decided to divide the fare between those two buckets. I assume you caught a nice fare sale where they lowered the base fare significantly but didn't touch the YR so you ended up with a nice J fare but the breakdown just happened to skew to YR.