How does least connect method works ?

The check is performed against pool members or node depending on whether you have chosen Least Connection (member) or Least Connections (node).

So when the LB decision is made the poolmember OR node with the least number of connections will be chosen.

In least Connections (member) the number of connections to the node isn't considered. Look in the admin guide (Google is your friend here) for an overview of load balancing methods and how they work, or the help in the GUI...