It certainly is! And that's why I think little details like the presence of a LINDA widget on Osgood's desktop right alongside the "real-world things" are of interest.
So is, as User:Najawin pointed out, the recent reveal of the fact that the writer, Peter Harness, holds the same broad views on "canon" and continuity in Doctor Who as the likes of Steven Moffat and Paul Cornell. Harness nearly put a line in the actual, televised The Zygon Invasion where the Doctor thought back to the Multi-Doctor Event "with Big Ron", and another where he recalled the First Doctor's perspective on being stuck in a time eddy in The Three Doctors as his having genuinely been trapped inside a TV screen.
Call the above "character evidence" in legal lingo — it would take a lot to get me, and I think any other fair observer, to believe that Harness's intent was for The Zygon Isolation not to be set in the DWU as he understands it, when he gave so many signs that it is set in the ongoing DWU (with the Osgoods' status-quo, the Thirteenth Doctor, LINDA and so on).