Maty Ezraty's reply:
There are many different teaching styles: Some teachers are serious, and others take a more easygoing approach. I personally believe that it is good to strike a balance. A little bit of laughter and talking can release tension and create a sense of community. Too much talking, music, and lack of order can be distracting and unproductive.
Yoga is balance. You need to find this balance with each of your groups, and with each student. Some students need more discipline, while some take everything too seriously and need to have more fun. Teaching yoga is like parenting: No two children are alike, and no two students are alike either.
I would add that intuitively I am reading into your question some concern that this group may have tipped the balance. If so, and you want to tip that balance back, communicate with them so that they are not shocked by your new approach.