Hergierr had been having trouble tracking Grimolf's footprints through the other footprints trekking across the road. Moving at a quick pace, you eventually reached the front of the north-bound travelers on horseback, just a handful of minutes before reaching this well-trod area. As you approach the intersection, you see the reason for the numerous footprints that cross the main road from the up-hill path to the east; directly opposite the smaller road is a shrine to Thor. A stone altar carved in the shape of Thor's hammer, standing upright with the hammer-head spreading to form a slightly curved table-top, is covered across its top with small offerings.
Hergierr looks at the tracks with his own eyes and can see that Grimolf's prints do continue north along the road, but they also show he made a journey up the slope to the village that must lie up the smaller road, before continuing north.
[spoiler]I find it odd that the tracking rules don't take into account a trail being over-ridden by a crossing group of people after the quarry has left his tracks. The best it does is increase the DC by +1 per 24 hours, which encompasses some of this idea, but there are certainly instances where a trail would be completely obscured. Granted, you can look beyond the crossing path, but there are times that would become difficult (though not here, admittedly).[/spoiler]