I don't want to say "slow" dancing, but Pinkie certainly seems like she's more fluid and perfectly in-tune with the music itself. Even if it's just the music in her mind. For some reason it seems like she's moving with a certain flow or elegance, despite the many streamers flying around. Could it be that you caught her in a single instant where we can actually see how harmonious her body and the music can be even when it seems like she's just dancing at full speed? Regardless, she's very lovely as she moves to the beat, however slow or fast it may be.