Head gasket, I had one that squirted a thin stream under pressure. I used the pump up tool on the radiator, almost 20 psi before I found it. Blue gel-pro gasket, almost new
This leak is from an engine sitting for three weeks with no oil pan. I can't imagine a blown head gasket would leak like this...especially since I saw no white smoke or lost any appreciable amount of coolant before I tore it down.
So you want to dispute the suggestion ???
Looking a bare block you don't have many other sources other than a head gasket or bolt.
It's doubtful an exhaust or head bolt leak would find it's way to the center of the motor.
So that leaves intake bolt (if drilled through), a head gasket, or the heater A/c system.
Is the back of the block inside the floor tunnel or in front of it. I might suggest laying under the car and looking straight up to see if their is any coolant hoses, heater /ac box etc. directly above the area of the drip. Leaks typically do not go sideways but rather straight down that is assuming they haven't a ledge or lip to follow.
Another thing to keep in mind, with the car sitting with the front raised up, the heater core, valves, hose connections are under more head pressure. HMMM
Or one could put a camera on it and possibly record the event and capture the source
Myself I agree with the previously suggestion(s) time for a pressure check
