There’s all sorts in aviation, including the commercial side of it. Some are more comfortable with a less strict regime, some find the rules perhaps a bit over the top sometimes but understand the overall benefit, some insist on going absolutely by the book, and others still think they know enough to write the book. One tend to find the more questionable representatives at either end of the scales.

What I’m wondering is why no take-off config horn was screaming at them as they set power. Is that not a feature in this flavour of Gulfstream?

Clearly the spoilers weren't armed or extended for takeoff - in other words there was a mismatch between the position of the spoiler control handle (presumably in the Retract detent) and the control surface (extended on one side only). Whether that would trigger a configuration warning or not isn't immediately obvious, but I suspect not.

I think the warning horn is a function of the handle poistion rather than actual spoilers on the model Gulfstream. Also, there are a couple of small mirrors that the pilot can see the physical position of the spoilers (I think?).