Sorry, but alive and dead are mutually exclusive. Alive is not dead. Dead is not alive.
What he meant to say was that there was no way to know the current state of the imaginary cat. He got confused. Words are so hard to understand.
You need to read a bit more about quantum theory.
Objects big enough to see (like cats) are indeed either dead or alive. But-- at least according to quantum theory-- at a subatomic level, minuscule particles are simultaneously in two places at once. It's not just that we can't tell if they are in one place or another; they are literally in both places at the same time.
Schrodinger's "thought experiment" was an attempt to ridicule this theory, but so far, evidence has tended to support the quantum theory.