I agree with TNrabbit it could be just talk.
I would think a somewhat plugged Cat Conv would raise more heck with the exhaust valves then causing premature headgasket failure.
I believe there are alot of 3VZE's that don't get the proper attention to the head surface when performing a headgasket. Or other engines for that matter.
I'm not yank'in my own chain but I have done quite a bit of work on foreign engines especially headgaskets. Generally they tend to allow 3 to 6 thousands of warpage across the head. Back in the 80's when I was working on hondas at a dealer,... if I found even .002 warp on a head, I sent it out. It's just not worth doing twice. And for saving what $38.00 for a resurface? This cut back on repeats, redo's, rework, or comebacks on headgaskets almost altogether.
It makes you wonder how many people actually do check head warpage "correctly" with an accurate straight edge like a Bluepoint or Starrett.
Their just not that expensive either, I think I gave $60.00 for 18" one which covers most head sizes back in the early 80's.
I have seen so called mechanics trying to use a carpenders square, and even a long 3/8" extention!
Makes me shake my head even now.
I know if i'm that far into any headgasket job it's worth taking the time and doing it right.
They aren't that fun to do, I don't care what engine it is.