"It" is unambiguously the correct pronoun to use for a car. I'd really challenge you to find a native English speaker who would think otherwise.
I would argue a computer program is no different than a car.
On the other hand, Claude presumably does have a model of the fact of not being an organic entity, from which it could presumably infer that it lacks a gender.
...But that wasn't the point. Inflecting words for gender doesn't seem to me like it would be difficult for an LLM. GP was saying that swapping "I" for "you" etc. depending on perspective would be difficult, and I think that is probably more difficult than inflecting words for gender. Especially if the training data includes lots of text in Romance languages.