The main difference I see is the starting point. Traditional link building usually starts with a target page and a link you want, while digital PR starts with a story, data point, or expert angle that a publication would actually want to cover. The link or mention is the result of the coverage, not the pitch itself.
A typical campaign tends to follow a few steps: find a newsworthy angle from the business, such as survey results, an original study, or a clear expert opinion on a trend; build a short press angle and a small set of target publications that cover that topic; pitch it personally rather than in bulk; and then follow up once. If the story is weak, outreach volume usually does not fix it.
For AI search, I would measure it differently from classic link building. Instead of only counting links, I would track whether the brand name appears next to the topic in coverage, whether the same facts or quotes are repeated by more than one source, and whether AI answers start naming the brand for related questions. Unlinked mentions can still help here, because AI systems often rely on repeated, consistent brand associations across trusted sources, but they are harder to prove than a direct link, so a before-and-after check of the same set of questions is useful.