Pay attention to the words. Fewer people buying stocks than selling. The amount of stocks "bought and sold" are the same, the amount of people is not. If what you are saying is true, stocks would always be at the same price since the amount of stock bought and sold are the same!

If one day there are 100 people that want to buy the stock, and the next day there are 10 people interested, the prices will fall.

They mean "fewer people willing to cross the bid-ask spread to buy a stock than the number of people willing to cross the bid-ask spread to sell a stock"; what matters is who is crossing the line? if it's the buyer side of the transaction, price trends up. If the seller is accepting a small % loss on the sale, the price trends down.