Yeah it's pulse air pipe, you can see the coolant pipe below it attached as normal. Most people delete the pulse air system, it is a crappy 1970s-era attempt at emissions reduction. This person has just been a bit lazy and chopped the pipe and capped it rather than deleting it entirely.
The temp sender for your gauge is located on the intake side of the engine, between and below the #1 and #2 intake runner, on the cylinder head. It will have one wire connected to it.