This doesn't make too much sense.
1) It's a very small amount of data.
2) The data is self-reflexive; it tries to be both the cause and effect. Of course Watford was most difficult to play when they won.
While I agree on 1) (not much I can do about that, it is what it is), I'm not sure I understand what you mean by 2). It's using the results in the opponents matches to determine how difficult of an opponent they were around the time the teams played each other. That's why I looked at their form over 5 matches, not just at the one particular match (actually considered using a wider span, but that would be too vague in my opinion).