High calcium levels can cause the pool to get cloudy, but low calcium levels will never cause the water to be cloudy.
Their business is selling things, of course they want to sell you something. If they don't know the reason why they need to sell you something they often just make one up. By and large they hire people with no training, who learn what they know by reading product labels. Every now and then you run into a sales person who actually knows what they are doing, but that is very unusual since they aren't paying enough to keep people like that.