Vertices order determines face orientation.
f 1 2 3and
f 1 3 2are 2 opposite faces
Another thing is, faces are invisible from backside by default!!!
In Meshlab here is a setting
back-facewhich by default is
single. If set it as
double, then the face will be visible from backside.
Meanwhile, the Preview of MacOS also makes faces transparent from opposite orientation. Like this:
Finally my sphere is correct: