|ov = $0D ; == $FF, initial value for the overflow counter|
|* = $0304 - (end - scroll)|
|scroll: jsr $AAD7|
|loop: lda #$A0|
|sta $D3E0 - $80, x|
|sta $0400+40*24+39-$80+1, y ; incrementing rower, y finishes with value $80|
|sta $0400+40*24-$7B-1, x ; decrementing rower, x finishes with value $7b|
The jmp actually saves a byte, as the two parameters bytes re-use the address in $0302/$0303. This address contains the "BASIC idle" vector. After a program has been loaded, the C64 jumps to the address stored in $0302/$0303 (which is now pointing to the start of this program). A typical C64 auto-start mechanism.
It's not just 6502/6510, it also relies on side effects of the KERNAL routines (I think $0d is loaded with #$ff as part of the C64 boot-up process) and it overwrites the $0302/$0303 vector, so the KERNAL never really returns from the LOAD to BASIC but starts the program instead)). It also spams many VIC memory addresses (the VIC appears several times in the memory map at "mirrored addresses"), eventually also hitting the correct addresses $d020/$d021 (which also appear at $d320/$d321) with #$a0 (which the VIC interprets as #$00 (= color code for black), as it only considers the lower four bits).