Sorry, but that completely misses the point. Question is not, whatever the VPN client program is doing - question is very simple, how can it be prevented to start automatically?
Obviously there should be some solution for this, as it is easily possible to stop the client from the menubar after it has automatically started. If I had been in charge of testing this software, it would not have gotten released - it is completely incomprehensible to implement a piece of software without allowing to configure whether it will start automatically or not easily in its GUI. *THIS* is the problem here.
I will definitely *never* recommend this kind of VPN client to anybody - no matter the features. Implementing software like this is just completely unreasonable. Please refer back to Software Engineering 101.