The “they” here is the procession with the Paul bearers. The procession is “proceed[ing] to walk,” not merely walking. We get an echo of police patois in this phrase. But the interest lies beyond.
I think that for this sentence my student actually did consult a dictionary. Perhaps he imagines the coffin (or Paul?) will be buried in a grassy clearing.
Probably he doesn’t imagine a knoll as a burial place, at all. Certainly that procession isn’t going to walk down to a knoll.
But he has heard the expression “grassy knoll.” He’s too young to associate the phrase with anything in particular. If he had Googled it, he would have been taken directly to the accounts of the assassination of President John F. Kennedy, and maybe even to this note about the person who first referred to the grassy knoll.
To pick up that trail, though, my student would have had to know that the word “knoll” begins with “k.” Searching for “noll” might have helped: Google lists “knoll” as a “search related to ‘noll,’” albeit only as someone’s name (Daniel Knoll). In fact, just about all the listings under “noll” are people’s names, too. So not a very big help.
Did my student begin by searching for “noll,” or even “nole,” or did he already know the word “null” (from math class, perhaps)? One way or another he got there. And we know what “null” means: without value; nonexistent; empty.
From here to the grassy “open space” is the shortest of steps. Not even an uphill climb.
I lament and bemoan my students’ reluctance to look things up, think about odd phrases, generally be aware of their word usage. And now here I am, bemoaning this student’s thought processes and, perhaps, research, which led him so logically to such a wrong choice.
I must seem to them a lot like the serpent (actually Alice’s very long neck, courtesy of the mushroom) that beset the pigeon’s nest in Alice in Wonderland: “I’ve tried every way, and nothing seems to suit them!…those serpents! There’s no pleasing them!” says the pigeon.