Supply/demand is a part of the price action of a cryptocurrency and in that sense the number of order at a particular price matters and once that gets executed next level of order will be filled. But that again gets decided by the people/participant on the market. The orders placed by the people world wide are again categorized like limit order and spot/market order. For example someone does not want to wait or put his limit and straightaway go with the market price, then it will be called as market execution. Similarly if someone wants to wait and put his own level and wait for the market to unfold and execute in the price sets by him. It is called limit order. But there is no guarantee that limit order will get executed by market, as supply/demand will decide that.
Someone is buying means that person is investing in to the cryptocurrency. So if the the people holding the coin does not want to sell at a lower price then definitely price will go up. Conversely if the investors want to sell either at market execution or by putting limit order, then based on supply/demand equation market will unfold. But the holder of the coin play a role in the value of a cryptocurrency as they are the people who will be selling the currency, so eventually they will set their price, although all will not set the same price, that is why it is called supply/demand equation.
There are limited number of sell orders on an exchange. These orders start with low price, but as they get filled up (ie. Other people invest) these orders will be disappeared and next order will become order with lowest price, hence driving price up.
Hope this makes sense.