The article says the following. "Trained logicians should know that semantic meaning is arbitrary...Abortion is the canonical example of [a semantic] argument: once you have decided what 'life' is, there’s really not much else to discuss. It’s not a political argument, not even in theory. It’s purely a semantic one."
So the author does seem to be saying that the whole abortion debate is purely a debate over arbitrary definitions, not merely that it's important to clear up semantic issues before getting into the meat of the debate.
If the issue were purely semantic, it would be possible to resolve the debate simply by introducing unambigious terminology agreed on by both sides (e.g. using 'alive*' and 'alive†' rather than 'alive'). If this doesn't satisfy both sides, then they aren't really disagreeing over the meaning of the word 'life', they're disagreeing over the nature or essence of life itself. Informally we can say that they disagree over what it means to be alive. But philosophically it's important to be clear that this isn't just a semantic issue about the meaning of a particular word.
Another way to bring this out is to think cross-linguistically. Do we really have to have the abortion debate over again for every one of the world's ~6500 languages and their corresponding words for 'life'? I think not, because at heart the debate isn't a debate over word meaning.