Are there signs posted on the doors prohibiting re-entry?
Often, those doors are open so that if someone e.g. needed help carrying luggage, someone could enter to meet the passenger and help pick things up. This assumes it's a domestic arrival area where passengers do not need to then go through customs.
However, most people are going out and you don't typically see people going in, because that is the natural traffic flow for arriving passengers to want to leave the airport on to their next destinations.
Even without customs/immigrations one-way flow, some airports may restrict access to the baggage claim area to reduce baggage theft, illegal taxi drivers pestering arriving passengers about rides, etc. (and some because they are concerned about events like this, but that was committed by someone who just got off the flight).
In general, if there is a restriction against traffic flow, such that you may not enter an area you just exited (e.g. to retrieve a forgotten item or person who seems to have gotten stuck behind), there should be signage indicating the restriction. In the absence of such signage, it is generally allowed to "swim upstream" and go the other way into arrivals; just watch out for colliding with others.
Typically, once you exit the security-controlled zone there is a sign like "once you pass this point you must continue to exit" and then you can't return back without another security screening. However, this is before reaching baggage claim (again, assuming domestic flight without customs).