Flip the xdot, ydot vectors and their sign
[x, y] = meshgrid(-2.5:.5:2.5, -2.5:.5:2.5);
xdot = (-1*x) + (2*y);
ydot = (-1*x) + (-3*y);
xdot = -fliplr(xdot); % <----
ydot = -flipud(ydot); % <----
figure(1)
streamslice(x,y, xdot, ydot, 'black')
grid on
xlabel('X');
ylabel('Y');
title('#2');
axis tight