Right, it doesn't mean anything.
Please do tell. Never heard of that, and it's what I'm driving... assuming that you mean double cab, as that is what Toyota calls it on a Tundra. The bigger one is a crew cab. They both have b-pillars.
If somebody mounts a rigid structure to the bed mounts... like pretty much everyone who puts a flatbed on a Tundra... then I can see that being a possibility, since the rear of the frame that is designed to flex the most, can't. Instead the middle (the part under the cab) flexes more. There are bed mounts that will take care of some of that, but they aren't designed for the rear of the frame to be rigid.
When the 2nd gen came out, boxed frames on pickups were not the norm. I don't know if any of the domestics were fully boxed then. The F250 (before it was redesigned in 2017) was particularly notorious. The cab mounts on those are sponge rubber and need to be replaced regularly. Same with the mounts on the E series van.
I see people defending against your unwarranted assertions.
If this just happened then speculating that the 2nd gen Tundra frame is crap could have some validity... but this was ~18 years ago! And they aren't crap, based on the opinions of most people who've owned them. And they seem to be a lot more popular with offroaders and overlanders than their sales numbers would justify.