The statement was more along the lines of scientific advancement does not always happen because a new theory is so obviously better, but that those who hold on, often viciously, to "old" theories, eventually die.
It was not a statement about whether the old theory was right or wrong, the statement accepted that the new one was correct, it was that old ideas often literally have to die, because the proponents who hold old to them, their life's work, often respected scientists, refuse to accept they were wrong (and what that would mean).
Flat Earth is not a theory, and barely a hypothesis, but perhaps a good example. The Greeks showed the earth was round in about 2,000 BC. Look how long it took some powerful organizations to accept that it really was round, and even longer to accept it was not the center of the universe, even though the evidence was clear to those that understood it.
I remember once reading somewhere that theories in science don't necessarily disprove and succeed each other - merely that when proponents of less popular theories die they often take their theory with them.
So even in science there is no absolute right or wrong, merely an accepted consensus which can change from day to day. Much like the butter or margarine debate which has seen both sides on top at one time or another. Sometimes even old forgotten theories eg Flat Earth, can attempt a comeback!