He is NORMAL.
Attachment to their Mommy and/or separation anxiety... is a very normal development. BUT also keep in mind, that this occurrence, is also age-stage related... AND it will occur at different ages TOO.
And per age, it will be displayed or manifested, differently. At at different moments.
This is normal developmental PROGRESS. Not a weakness.
It would be more "abnormal" or concerning, if a child never... went through this. That would be an "attachment disorder."
Kids, even if independent... are attached to their Moms, and go through separation-anxiety.
Some have this happen, at even earlier ages than 1 year old.
Kids also get like this when:
not feeling well or are sick, or when getting sick
when they are tired
When their life changes somehow or their routines
Or when teething and uncomfortable
Or when stressed
Additionally: this has to do with the concept of "Object Permanence."
Which is a normal developmental thing, that this age or younger goes through. The idea that things that go away, comes back or that, what they do not "see"... still exist.