Poems in general tend to pull in a lot of different threads. They might mention a couple things that seem pretty unrelated; then, as the poem rumble along, you realize that everything starts to fit together. That's part of how poems achieve depth, and it allows them to approach things from different directions. But Tony Hoagland has a pretty distinctive way of jumping around in time, place, and focus.
The best way we can think of to describe it? Juggling. Take "Reading Moby-Dick at 30,000 Feet." He starts with one setting: the view out an airplane window. He throws that bowling pin up, and soon brings in other one—his feelings. And watching him juggle the two, we might notice that they both have to do with distance.
Then comes the next bowling pin: his childhood memory. Our focus soon turns back to the plane, and to his distraction, but we've got all three pins up now, and we're starting to see how they all relate to how he's come to be dissatisfied with the inactive, detached life he's leading (or, rather, not leading).
Then he adds the imagined scene based on Moby-Dick. And we see how it works in as a sort of opposite to our speaker's life. And then there's yet another pin: his musing on modern life as a long corridor. Still more depth, more ideas working together.
So when we focus back on the scene from his book (at the end of the poem) the other settings and ideas are still there, like pins spinning in the air behind it, adding depth and expanding our understanding of that scene.