It is very common that when leaving home we take advantage of a moment of distraction of the child to open the door and disappear as if by magic.
Sometimes we even cause him to be distracted by someone to escape before he realizes we have taken the keys and the bag to leave.
A small child does not understand why a minute ago he was with his mother and suddenly it turns out that he has disappeared. Naturally, generates great confusion in the child He starts asking about his mother (or father) without understanding if he will return or not, for how long and why he has left. It would happen to anyone if we are with someone and suddenly we turn around and disappear.
The separation of the mother is not a minor issue for the baby. In most cases it is his "special" person, his reference to the world, and like everything else, he needs to gradually learn to separate from it without trauma.
I think it is much more natural and reasonable, even if he is small and we think he cannot understand us, say goodbye with a kiss and explain that Mom has to leave 10 minutes, a few hours, goes to work or travel. It is very likely that the child does not like anything you go and probably cry, but it is normal (and healthy) to show his feelings.
It's more logical that I miss you because you're going to feel insecure about the sudden disappearance. The child does not know if you will return or not to fade away, but creating that farewell ritual can associate that you leave but then come back.
Farewell is important because it helps the child to better assimilate the separation process. Then there are children who, in the face of minimal separation, cry as desperate. It is also less distressing for the mother (or father) who leaves home knowing that she has not used tricks to fool her baby.
