That's correct. The ball release coil is switched by a MJE2955 transistor under the playfield which is triggered by Lamp Signal L12 via transistor T13 (MPS-U45). Gottlieb did this because there weren't enough transistors on the driverboard to drive coils directly, So they used this workaround via transistors originaly meant to drive lamps.

That blob of solder is the so called slam switch mod. It disables the slamswitch as the normally closed slamswitch contact can cause problems over the time. Gottlieb later ( around Excalibur, Big House ) applied a normally open slamswitch at the coindoor to avoid this problem.