HTupolev

If it goes past River Meadows Park, he's referring to Jordan Road. It roughly parallels the South Fork Stillaguamish river between Granite Falls and Arlington, on the north side of the river. Burn Road plays a similar role on the south side of the river, although it's more atop a ridge and mostly far from from the water. Both roads are reasonably fun to ride in the southeast direction, although I think Jordan Road is definitely more fun in the northwest direction.
It's possible to cross the river at Jordan River Trails midway between Arlington and Granite Falls, if you're on foot or on a bicycle.

Jordan Road is paved. There's a lot of gravel in the Cascades near Arlington and Granite Falls, but not really any gravel routes between the two. As far as I know, there might not even be any extant connections between the Mountain Loop Highway valley and Highway 530 by way of the Weyerhauser land behind Jim Creek, but it comes FRUSTRATINGLY close. Here's a photo from a ride that started on the Mountain Loop just outside of Granite Falls:



This was taken right by Wheeler Mountain and that's Oso down below.

grrrrrr