I think you're confusing the boundary of the visible universe (the limit after which light cannot have reached us yet) and the unmapped volume the poster is tal

I think you're confusing the boundary of the visible universe (the limit after which light cannot have reached us yet) and the unmapped volume the poster is talking about, which is inside this boundary. Alpha Centauri was emitting light just fine 4 years ago so of course it can be mapped.