This just sounds like a misuse of the word truth. It's common for subjectivists to attempt to dilute the meaning of the 'truth' by misusing in various ways. Using Newtonian physics or general relativity does not result in multiple truths. Using different equations to calculate the area of a function may result in different values but the actual area of the function is objective.
Quantum physics does raise some questions and there certainly is multi-valued logic in math but I've yet to see this translated into anything that would support subjectivism.
"When pressed, quantum theorists usually fall back on what is known as the Copenhagen interpretation. The idea was promoted in the 1920s by Danish physicist Niels Bohr and his protégé German physicist Werner Heisenberg. In their view, we do not see quantum effects in the everyday world because the act of observation changes everything, fixing the many possibilities allowed by quantum mechanics as one. As a result, when we look, we only see one version of events, with every object firmly anchored to one position at a time.
The flaw in the Copenhagen interpretation is that it has no basis in theory—it is more like a story that scientists tell to make sense of facts that otherwise would seem nonsensical. It also suggests that the universe does not become fully real until someone observes it. Einstein found this idea abhorrent. “I like to think that the moon is there even if I am not looking at it,” he fumed in response to Bohr. Nevertheless, the Copenhagen interpretation was voted the preferred explanation of quantum weirdness by physicists at a conference in 1997."
If an Electron Can Be in Two Places at Once, Why Can't You? | Subatomic Particles | DISCOVER Magazine
Even in the many worlds example, there is always an observer. At no point in your life will this ever create an issue. To the observer two valued logic will continue to work the exact same. So even if Schroedinger's cat's life really is in some third indeterminate value at some point, once you open the box it doesn't matter anyway. Of course Schroedinger used this as a reductio ad absurdum to show how QM doesn't apply to real life.