I've seen conflicting reports about this, including a claim that people are faking it by blowing smoke into the unit using vape pens.
HAHHAHHAAHAHA!
Looking at that twitter handle tho, take with grains of salt. Either way, if Series X does have problems with thermals, no doubt that will become clear over the next weeks/months. One would expect it to have safeties that would shut the unit down long before it ever gets hot enough to start smoking, but, you know, it's Microsoft. They've been known to cheap out on various hardware components in the past.
Reminds me of a case of a PS5 overheating at a Best Buy display for real
But that was cuz those geniuses put it in a fully enclosed and unventilated plexyglass box. And of course, it does have a safety, which did kick in.