It's a bit of "technically true" mixed with a bit "take a look at it realistically."

The amount of leeching in soil would be quite minor and not very horizontally mobile in the beds.

Your biggest issue with treated wood would be from direct human contact (mostly direct contact followed by ingestion...such as handling the wood then eating something with your hands without washing your hands). Even with direct contact it's a constant ingestion thing that would be a concern more than an occasional incident because of the low amount of residues involved.

If your wood is old and flaking away with the wind/weather, wash your produce before consuming because of possible external contamination. This shouldn't be much of an issue because most people do this anyway even when there's little/no threat of contamination.

As far as the roots reaching the wood and uptaking "bad stuff" via contact... it's not much of a concern for almost every vegetable crop, especially fruiting and above ground leafy crops because of how well the roots and plants, themselves, exclude a lot of "bad stuff" by natural design.

Railroad ties, sleepers, will leach the creosote they are treated with into the soil, but it does not migrate very far and plants do not uptake that stuff. The Chromated copper arsenate, CCA, treated wood leached Arsenic, but the problem with that was that people could pick that up on their hands and possibly ingest it, children especially.
As a general rule of thumb an organic grower will not use any treated wood in the garden.

is it just a claim they are making to sell their product?

Basically, yes it is.

I'm all for recycling but recycled plastics - what it is made from - are not any more chem-free than many woods are.

Dave

They do say that the plastic used is non-toxic, and the 50 year life span is certainly appealing.

Not sure I'll be around that long though! :P