Initially, I thought this might be a void that's at the surface. I believe that there is always the chance of a void, or a hole, in carbon fiber, but good manufacturing will minimize the incidence of voids. They would weaken the structure. The manufacturer designed that area to have a certain strength, and now there's a hole in the middle of the tube (or at the surface, in this case). Based on that, I would probably check my warranty options. If they refused and if you were sure you were lowering the stem, then this might be not so bad.
I'm a member (i.e. customer) of the Escape Collective, which has a Discord. It turns out that Raoul Luescher, a notable carbon fiber repairer based in Australia, is on the Discord as well. He would know better than I, and he felt like this was a scratch - although remember that we are on the Internet and he is making a visual diagnosis by remote (whereas he would use ultrasound to examine a frame). If it's a scratch, that could reduce your warranty options. Keep in mind that a scratch might propagate through the steerer as it gets stressed during riding - of course, I'm not sure if a void might do the same. In any case, I think that damage is probably more concerning than a void (or another similarly pre-existing failure).
I wrote this answer and then saw your comment that the manufacturer offered to replace the fork. I would go ahead and take the replacement. I don't know the probability of failure. But even if it is just a bit higher than the probability of a normal steerer failing in use, if your fork fails you are going down and those sorts of injuries can be quite nasty. Since the replacement is free, I would take it to minimize my risk.
