Aliens exist in the same physical universe that we exist in.
However we only engage directly with a small subset of the universe and in ways that have been evolutionarily useful.
Aliens might well have evolved to engage in a different subset.
We certainly have different subsets here on Earth -- consider colour vision for example and the effects on colour coding interpretations between humans, fish, birds, reptiles, bees, etc.
Communication requires being able to predict response to stimulation. The degree of similarity with which we perceive a given stimulation will determine how well we can communicate.
Computer programs can been seen as a kind of communication with a computer, and it only makes sense for programs to be written in a convenient communicative form.
While it might seem obvious that aliens would use digital computers it isn't necessarily so.
Analog computers might make more sense for them -- the main reason we don't use them much these days is that they're hard to reprogram -- but with nanotech or biotech it might be far more trivial.
There are also quantum computers, and non-electrical computational systems.
People also assume numeracy, but consider aliens without recursion which deal with numbers by subitization up to some large quantity rather than counting.
If he kept that word intact his argument would collapse.