Between observing and listening, I perceived these sounds very differently. As an observer, my brain filtered out much of the chatter as background noise. Voices and laughter blended together into an ambient babble. Very little stood out, apart from the occasional high-pitched laugh or clink of a bottle near me.
As a listener, on the other hand, the context was quite different. Hearing these sounds with headphones in a quiet room, I perceived the background noise as foreground sounds, with much more focus and attention. Every divergent pitch (high or low) stood out twice as much as it did while observing, and my brain even attempted to pick out patterns in the din. Ironically, while listening, I completely ignored the real sounds around me (ruffling of paper, and a quiet conversation in the back corner). As such, I believe the difference is mostly due to context and attention.