I've heard some other K3s splatter. QST measured the transmit 3rd-order IMD at -29 dB. That's pretty horrible considering some rigs made 25-30 years ago were at -35 or better.
I've heard several folks mention this, but his signal on 10 was okay when I heard him. I tuned above and below listening to other stations. Maybe he cleaned things up.
Then again, when you take a bunch or pre-assembled boards and shove them into a box (or as Elecraft calls it, "Modular No-Soldering Kit"), anything could result. It's a far cry from something like a Heathkit that you actually built up from the component level, aligned, and proceeded to troubleshoot as needed. One step away from buying a Yaecomwood.