This is simply not true. If a cell would not behave as intended on average it would stop being a cell.
The fact is that an amoeba cell behaves in a certain way for all amoebas. It does not go around and behave like a stone or like a drop of olive oil or even like a cell of some random bacterium.
It has very clear and obvious functions and the mechanisms inside the cell are the reason it consistently shows amoeba behavior.