Why React.memo and shouldComponentUpdate aren't doing the same?

I have a functional component which has has a connection to an object in my Redux store. To avoid re-renders when the object has changed I added React.memo, however, this didn't avoid the re-renders. My Memo looks something like this:

const MemoizedRadio = React.memo(Radio, (prevProps, nextProps) => {
  if (prevProps.selected !== nextProps.selected) {
    return false;
  }
  return true;
});

const mapStateToProps = state => ({
  nodes: state.canvas.elements.nodes
});

export default connect(mapStateToProps)(MemoizedRadio);

I would expect this component to not re-render if the nodes object has changed, but it does.

When I rewrite my component to a class component and add a shouldComponentUpdate the re-render will be prevented as expected. The shouldComponentUpdate looks as followed:

shouldComponentUpdate(nextProps) {
    if (this.props.selected !== nextProps.selected) {
      return true;
    }
    return false;
  }

I thought that React.memo acted the same as shouldComponentUpdate but this does not seem to be the case. The React.memo implementation does always re-render when the reference to the nodes object changes while the shouldComponentUpdate implementation prevents the re-render as expected.

Can anyone explain this behaviour?