Yep, the hot throttle linkage is classic sign of failed ground strap to engine. Thus you having forgot to reattach the bonding strap/wire would be accurate. The engine mounts are rubber so the engine is really well electrically isolated from the chassis without a bonding strap. All the electricity trying to flow through the starter followed the path of least resistance the throttle linkage which isn't a very good conductor because of all the gaps between the parts. If you were so inclined you could even throw on a couple extra bonding straps besides the one so if you lose one there would be another.
Attaching to one of the starter mounting bolts is good, but you can attach additional bonding straps to anywhere on the engine. Chassis to engine side motor mount bracket bolts for example because the engine block is a great conductor as long as there is a path back to the chassis.
Walker
1968 Series IIA-"Ronnie"
88" SW, 2.25L Petrol, LHD