If you observe something that has many of the same properties as an apple but you don’t know where it came from, you have observed apples growing on apple trees, then the most reasonable scientific hypothesis about the origin of the apple-like object is that it was produced by something like an apple tree. Indeed, to hypothesize that what you found just spontaneously formed on the ground from inanimate matter would be entirely unsupported.
For the ID hypothesis stated in terms of Karl Popper’s scientific hypothesis of white swans
The only abstract coded information processing and manufacturing machinery where the origin is known is a product of human intellect. There is one other known instance of this type of machinery, it’s found in all in living things, and its origin is undetermined. We only have one confirmed producer of these kinds of machines and the producer is human intellect. The most reasonable scientific hypothesis is that machines of unknown origin were produced by something like a human intellect.
This leads to exactly the type of scientific hypothesis that Karl Popper exemplified with white swans.
Popper’s Hypothesis: All swans are white.
ID Hypothesis: All abstract code driven information processing and manufacturing machinery, which isn’t simply a replication of prexisting machinery of the same type, was produced by intelligent agency.
Popper’s hypothesis, he said, could never be proven because there could never, even in principle, be a way of knowing that a black swan doesn’t exist somewhere. Popper said the key thing that made it a scientific hypothesis was that it could be falsified in principle by observing a single black swan.
ID’s hypothesis can never be proven because we can never know, even in principle, that no non-intelligent process is able to design these kinds of machines. ID’s hypothesis however can be falsified by observing a single non-intelligent process creating these kinds of machines.