You can also try using a couple of the DMVs to determine the IP address of the originating server, then work with your network team to find the computer name.

The script below should pull the information:

use [master];

go

select sdes.session_id

, sdes.program_name

, sdes.login_name

, sdec.connect_time

, sdec.client_net_address --This is the IP of the SSRS server

, sdec.local_net_address --This is the IP of the SQL Server

from sys.dm_exec_sessions as sdes

inner join sys.dm_exec_connections as sdec

on sdes.session_id = sdec.session_id

where sdes.program_name = 'Report Server';