I would guess Larson wasn't a fan, and thought that "new age" practices were mainly performative and non-productive, leading practitioners to get stuck in repetitive little circles, getting nothing done in the end.
If so, it's a pretty cynical take IMO, and certainly one of his more personal, brassy ones.
I think specifically "new age" here is referring to water-divenation, this is where some person claiming to be able to detect water gets a divining rod, which is often just two sticks and claims the sticks can show them where to dig a well and hit water (you can look up videos of it on YouTube). They often walk on strange paths, or stagger around and around fields in this process.
So I guess these guys are doing something similar with construction related tasks.
EDIT: I've seen it suggested elsewhere that Gary Larson was particularly annoyed with New Age music, and found it repetitive:
No one seems to get this one, at least on the internet. The most likely interpretation I could find anywhere is that he's referencing crop circles. Which kinda works, but also not...I'm not sure that's it either.
Heard a story the other day about a plumber who dowsed to find a water leak in an outdoor pipe.
Had to bite my tongue to stop myself from pointing out that the teller of the story unconsciously mentioned that the water leak also happened to be in the exact spot where the grass had been growing faster than the rest of the lawn in recent weeks.
To me it is the misframing of it that is the problem:
IF a person holds 2 bent wires, or a pair of sticks, or a y-shaped piece of willow, or whatever, & they walk around & to them it feels like something's going through it when they're over moving-water or moving-electricity ( I've a relative who tells me he can't tell the difference between the 2, from the dowsing: they give him identical signal )..
THEN you can't claim that it is some property-of-matter-divorced-from-their-unconscious-minds!!
THEY are the ones doing it: THEIR unconscious-minds are immersed in all they are doing.
If their unconscious-minds can somehow make accurate determinations, and communicate that determination through the "feelings" they feel when holding their dousing-rods .. how is that pseudoscience?
Scientism's falsely pretending to be Science bugs me.
The prejudice encoded in "matter cannot produce that result, & OF COURSE their minds have no validity, ESPECIALLY THEIR UNCONSCIOUS MINDS.. so therefore NO kind of mind can possibly have any place in the scientific understanding of anything.."
..prejudice isn't Science.
IF a phenomena is produced by a mixture of mind & matter, especially a mixture of unconscious-mind & conscious-mind & matter,
THEN correct science has to study each of the dimensions of the system, correctly, & the way they're interacting.
Prejudice, however ideologically-"proper" or currently-fashionable, isn't Science.
Anyways, I'll never expect to see the "skeptics" do proper science, when their physicalist-existentialist ideology can "solve" everything much more conveniently, to them..
Ideology & prejudice are inseparable: they're opposite sides of the same "coin".
I too don't know what this means. After much searching I believe this could be a reference to the whirling dervishes of Sufism. More likely than dowsing in my opinion.