I don't think you've ever defined sweaty. If you can't, you can't. But it'd be more helpful to us if you could show us what you mean.
He's talking about a term I've thrown around in the past to refer to a certain intense quality of writing. 'Sweaty' describes both the writer's state while writing it (in my case literally) and the effect it has on the reader.
An obvious opportunity for sweaty writing is an intense, high-stakes scene where some rapid, dangerous action is taking place in a difficult setting. There's lots of opportunity there for sharp, hard language, vivid images, blood-rushing events. And in fact, that's where I first encountered sweatiness as a writer.
I think as one progresses, the nature of scenes where sweatiness enters the picture widens in scope. It seems to me that there have to be stakes in play to reach that high pitch, but not having money to pay the rent can be high stakes. There don't have to be zombie gnomes beneath the steam heater.
What I'm getting at is an intensity of language and scene which captures the attention in a vivid way. It's the opposite of competence, if you will.
A competent scene tells the story, advances the plot, describes the setting, etc. Pretty much everything ever published that's worth a damn is filled with competent scenes. The stuff that isn't worth a damn consists solely of competent scenes.
The sweaty bits are the parts that stick out above the competence, the peaks that the valleys of competence are intended to help you recover from.
A few works are almost entirely sweaty. Veniss Underground and Vellum spring to mind. That's difficult to sustain as a writer, and it's hard on the reader. The grab-you-by-the-throat-and-don't-let-up thing can be merciless. Fascinating, but sort of like sprinting your way through a marathon.
At the same time, fiction without sweatiness devolves to blandness. I don't want my fiction -- as a reader or a writer -- to be a millpond. (Which is one of the traps of polishing, as well what someone referred to in comments as "crit burn.")
I'm still not sure I've adequately definied "sweatiness" in writing, but it's one of the things I treasure most in my craft and in the craft of others.