@LV-04
Contra-ry to popular belief, the start button is not part of the Konami Code. The game only checked for up-up-down-down-left-right-left-right-B-A. At that point you got your 30 lives and the Start button… started the game, as it always would.
-snop-
Most old games would keep all sorts of gameplay variables in memory even when not actually playing, using a mode variable to determine how to react and what to draw. Therefore, the title screen would know to react to the Code and set the lives counter to 30. This sort of system is also easily seen in Super Mario Bros 1, where the title screen itself is also the attract demo.