There are few maps from early 2002 to May 2002, when e3_strider was made. It seems that striders didn't have an AI initially, their models were just cyclers and Valve put func_tankrocket on thir hulls to make them look like they're firing (e.g. c17_ruins03.vmf).
Then by the begining of February of 2002 they added an ability for them to navigate and shoot (check dock_strider.vmf and strider_street12.vmf). But it wasn't some scripted sequence that mention immolator, it was a simple trigger that set a relationship on some npc_bullseye.
There's also an entity called 'info_target_immolator', not sure what that does. Maybe VXP will give a hint and tell us is there's any leftovers left in the code.