I am anything BUT a professional programmer but I was programming in BASIC from 1982 and built a lot of home-brew versions of games from breakout to battlezone BITD. The simplest, most efficient, and most resource-friendly way I could conceive to program an attract mode for a game would be to have a routine running the game routine for a fixed time (ie from a starting point to an ending point) with "control input" data read from a file. Whether or not the [main, attract mode] routine feeds the data to the game routine, or that the game routine's control input polling subroutine contains a switch variable which during attract mode forces it to read from the file instead of from the joystick, buttons, etc., is a matter of preference and, most importantly, efficiency in time. In either regard there is all but certainly a file of numeric data representing control input and this data is read by the game routine as control input during the attract mode routine.
The question is, does the programmer choose to author said file manually, or to record a segment of game play and use this data as his attract mode file? 10 seconds of 1982 attract mode time could necessitate up to (and maybe greater than) 600 units of numeric data, data resembling: 11111222333888844477733333383626190000006346101625610333334444444057623409123089..... or the like (which, yes, ultimately would be converted to binary; still, the programmer would have to enter it in legible form, first). Personally I would rather, during the final design phase of programming the game, write and execute a routine that would record, during my playing of a run of the game, the control input and write this data to the questioned file (to be read from on "playback" during the attract mode routine). Irregardless as to how much this might slow down the execution of said process. (Today it wouldn't be noticeable; in 1980 it may have been.)
Blah blah blah.
Yes, imho it would always be FAR faster and easier to record the control input than to enter it into a file manually. Unless playing on a 10-key is WAY more fun than playing the game in question, in the first place. In which case you aren't going to attract anyone, anyway.