What sinistersister is trying to tell you is that the money may have been held in what is called a constructive trust, meaning there is no written document establishing the trust, but there may be facts that establish it.
As you can suspect, proving such a trust is difficult.
But, for example, if Granny says at Christmas dinner that she put Suzy on her million dollar checking account as POD so after she (Granny) goes, Suzy can just split it up equally among everyone at the table and then Granny falls over dead (knocking the turkey to the floor in the process), there might be a constructive trust and everyone has to go to McDonald's to finish eating.
This kind of thing is done all the time by people trying to avoid going to lawyers and doing all that fancy estate planning stuff. It's quite risky, as you can well imagine.