There are a couple of point to make here.
The annotation to rule 13.8 says that “The official spot is just next to the line (since the line is not part of the playing field), but a pivot foot on the line is also acceptable.”
If the thrower had established a pivot at a particular point, and the marker had started to stall, that indicates they were happy with the pivot location and it would be contrary to SOTG to wait until after the throw to call the travel.
Also, the thrower can be touching the OB area, as per 11.3.2.: “A thrower in possession of the disc, who contacts the playing field and then touches an out-of-bounds area, is still considered in-bounds.”
In addition, the marker should only call travel as per 1.3.: “only make a call where a breach is significant enough to make a difference to the outcome of the action”.
However if the thrower traveled in such a way that it would be called regardless of whether they were now out-of-bounds, then it could be a reasonable travel call.
As always, it is hard to tell without seeing the actual play, but hopefully this gives you some ideas about how it could be officiated.