Yes, but it doesn't matter. The foam really acts as a spacer to convert a single block of concrete into two blocks separated by a few millimeters.

As soon as the concrete is set into place, the foam has done its job and can degrade all it likes.

Interesting! But what holds these blocks at the separation once the foam is no longer load bearing ? Some external bracing ?

Typically the foam is only in the middle of the concrete slab, so there are still a few inches of attachment all around all the edges with contact. There is rebar in those edges too.

Interesting, do that's how it works - thanks for the explanation! :)