wrt to the will of the creatures, the statement is directed against Arminian accusations that Calvinists don't believe in free will. We do believe in free will, but not the same kind of free will that Arminians and Socinians believe. They believe that free will means the ability of contrary choice: I can choose to do an action or not to do it. I can choose to please God or not to please God. Calvinists do not believe in this kind of free will. Rather, we believe that free will means that a person can do anything that it is within that person's nature to do. If a person is a sinner, then he is not free to please God. Rather, he is free to make free choice among several sinful options. Obviously, if the Arminian definition of free will were true, then God is not free, since God cannot sin, which He would be able to do if He had the power of contrary choice. In other words, free will is defined by the character of the person.
The second part of that statement has to do with rejecting hyper-Calvinism, which states that there is really no need for evangelism (for instance), since God will convert that person anyway. This really does make people into robots. The correct interpretation of God's sovereignty is that He uses any means that He chooses in order to accomplish His desire, including missionaries, etc. That means us. Therefore, we (and the means of grace) are the secondary causes, while God is the primary cause. God's sovereignty therefore works through secondary causes sometimes (actually, most of the time), and without secondary causes sometimes (as in miracles). But the latter does not deny the former. Hope this is clear.