First of all welcome to GMing.
Really in this situation the most important question here is, "are your players having fun?" If the answer is yes, congratulations, you've done your job.
As far as you deciding on how the dice roll turned out, that's fine. But instead of calling them losers why not weave the reasoning into the story? You caught them exhausted after they trained or they just had too many rounds of drinks.
You're the GM. You get to decide what's legal or not. At the end of the day the core rules are not a bible but a guidebook to go by. See my first thought of are they players having fun? Yes? No worries.