The FOMC certainly lifted crude on Wednesday (3/18), but the front month outperformance actually happened on Thursday and Friday.
Here are the closing prices for 3/17, 3/18, 3/19, and 3/20:
CLJ5: 42.43, 44.69, 43.85, 45.87
CLM5: 46.37, 48.8, 47.54, 48.34
And here are the daily changes for 3/18 - 3/20:
CLJ5: +2.26, -0.84, +2.02
CLM5: +2.43, -1.26, +0.8
The beta hypothesis would have had CLJ5 outperform on Wednesday (didn't happen). The price action on Wednesday doesn't support the FOMC hypothesis for narrowing contango either.