I would go beyond the fact that we understand Mr. Woodhouse never thinks ill of people and only comments about them in a favorable light, and say that we are also made to understand the slightly selfish aspect of his personality which makes him an unreliable narrator. His view of the world is very narrow. He sees everything through the prism of his own few priorities (health and stability, mostly). We see this in many statements, but to take the one you quote:

"I wish you would not make matches and foretel things, for whatever you say always comes to pass. Pray do not make any more matches."

It seems Mr. Woodhouse cannot imagine Emma did not indeed make the match, so he comes up with a peculiar explanation and solution to what he considers "a problem" (a change in "his" world order). I can't decide if he is a bit senile, or a hypochondriac, or simply naive in that he cannot imagine people would do anything other than be frank in their deeds. It's probably a combination of the three. In any case, I believe this odd remark allows us very early on to understand not only that he is not a reliable narrator, but also that his particular psychology taints everything he says.