these are two different creatures in front head area. all the shapes of a "face" are different, everything about the skull and its parts - forehead, jaw, mouth, nose, cheeks and so on. if they were people, nobody would say they even look alike, and definitely wouldn't say that's the same creature. they just have different head shapes and different faces.
opening the Neca's mouth won't help, because a) it will move the silhouette and shapes even further, and b) original alien's mouth is already opened.
for example, this is a "perfect copy" from Neca - toy versus movie, toy looks like sculpted from that very screenshot.
and that "alien" is as random as tsang creatures.
when other points of view are compared, other differences are seen, the main thing is that alien head widens in its center strongly and toy's head almost doesn't change its width, the forehead part is too small, throat is ridiculous, mouth looks like a bat and so on.