I see what you mean now. Currently, Xeams does not print the output of the external tool in the reason. This is done by design for the following reason:

The External Tool rule can be used for several reasons. It is not limited to running a third-party virus scanner. For example, a company could automatically process incoming purchase orders based on the attached file. The ONLY way to print the name of the virus is to print the entire output of the application. Depending upon the application that is executed, this output could be very long and printing the entire output in reason is not practical.