Looks like a memorized route to me.
Or maybe i'm just interpreting streaming wrong but isn't it supposed to be the art of minimizing the threat of a rapid barrage of aimed bullets by "streaming" them slowly from one side to another?
EDIT: Now with Touhou Wiki quote.
"Streaming, or herding, is the basic principle of controlling bullets in danmaku shooters. The majority of the enemy shots are aimed directly at you, so by standing still, you're effectively luring the enemies to shoot at the spot you're in. To take advantage of this, move as little as possible so that you can gather all aimed bullets in one tight stream slowly following you from one side. This way, you can dodge most of the incoming bullet bursts with just a small tap away from the stream, giving yourself more freedom to move in case of emergency.
To change the direction of the herd, do a quick move away from the stream (called "jerk" or "cutback") to make an opening, wait a bit to let the enemies readjust their aim to your new location, then proceed streaming to the opposite direction. It is advised to make cutbacks perpendicular to the stream source to increase the size of the opening (i.e., if the majority of the bullets are shot from the center of the screen, and you're streaming from left to right, cutback diagonally towards the top-right corner of the screen). If you're doing it right, the opening will be large enough to let you go through, no matter how dense the bullet stream is.
The more experienced you get, the more calm and confident you become about the streams and going through openings. As such, the technique becomes the key to evading most aimed attacks; danmaku shooters developed by Cave popularised the U-shaped movement pattern based entirely around streaming and doing cutbacks at the edges of the screen to be able to survive the bullet onslaught during the stages.
Streaming is commonly used when moving left or right, although purely vertical streaming does exist. Some cards where streaming is essential include Sakuya's, Yuyuko's, and Kaguya's.
This technique is the key to getting many graze points from any streamable attack. "