Siddimaula

That was the second point in my post.
2. In monopolistic competition as new firms enter the market, each with thier own differentiated product, they eat into the market share of existing firms. Thus the demand for products from other firms is reduced and the Demand Curve for product of other firms shift to left, thus decreasing their equilibrium price.
For example, you have a firm that produces pens. Another firm B enters the market with supposedly better features in their pen. Because of that demand for your pen reduces, even though you did not increase prices for your pen. This is explained by downward SHIFT in the demand curve for your pen.
In another case, if you had increased prices for your pen and as a result its demand was decreased, it would have been because of movement ALONG the demand curve of your pen.