I will offer a few points for your consideration.
First, I believe you may be over analyzing. It's a common phrase, typically someone isn't applying it in a rigorous fashion and inspect the definition of each word to apply a hyper-specific, qualified meaning.
Second, it's "nonsense" if you share the same assumptions, but not if your initial starting place is different. I assume you don't believe in God (please correct me I've misjudged), or if you do you have a conception where He doesn't intervene in the natural order, but that's not where everyone else comes from. If you believe that God intervenes in the world and you have a relationship with God then it makes sense to trust Him.
Third, from a theistic expression, I'm personally most familiar with Christian expressions in particular, one would trust in God because: one, God is a just judge, in a life and death situation where you will, to utilize a common phrase, "meet your maker," it makes sense to prepare yourself for that by entrusting yourself to "your maker". Two, by trusting in God you will calm yourself, you are able to resign yourself to do what needs to be done and be content with that because you are in right relationship with God.
I completely understand that if you don't understand the common phrases meaning or don't have the same beliefs, but then I don't think the "nonsense" would actually be the phrase used, it would be the prior beliefs that lead to it.