Not exactly, people moving without trying to take control is just settling, when they try to overtake control instead of assimilating into the culture they immigrated to then I think it can be considered some form of colonisation.

In The Prince, Machiavelli describes the use of settlers to exert indirect control over an area. One benefit of this approach is that the values and attitudes of the settlers will spread to or exert influence over the locals. At the very least, it destabilizes the existing order.

If a group doesn't assimilate, it looks like a ghetto or a "colony". Settling, on the other hand, is inherently about control.

How is settling different from colonization? Seems to be synonyms to me

Settling doesn't imply control, it's just people moving to a place and settling on it; colonisation is the act of taking control of an area, which settling can help to achieve.

They are not synonyms.