At time 0, the term multiplying dZ is zero if we buy the recommended portions in the result of the problem.
But at time t > 0, the stock prices will not be the same as there were at time 0, therefore the term multiplying dZ would no longer be zero.
And this will not be a risk-free porfolio.
What is wrong with my reasoning?
S(0) - Q(0) = 0 =/=> S(t) - Q(t) = 0, for t > 0
