I don't know the game, but from what you say it sounds like Polling-based multitasking to me.
Polling based multitasking doesn't use real multitasking, but handles the multiple tasks timeline or event controlled.
A very simple example is:
while not keydown(1)
y1=y1+15
y2=y2+17
if y1>200 then y1=0
if y2>200 then y2=0
positionentity s1,-1,y1,5
positionentity s2, 1,y2,5
wend
y1 and y2 are moving individually and simultanously, but not with the same speed. Although it looks like the puter is doing both at the same time, it's doing it one by one.
This way you can do much more complex things, you only have to take care that none of the tasks will branch to an endless loop by its own and therefore freeze the polling loop.
Basicly all (pseudo-)Multitasking on the OS level is done this way, as long as it isn't processed by a coprocessor or non-cpu device. EG. the soundcard chip will play a WAV using direct access to the ram, so the CPU won't get dirty hands from the WAV at all, this is real Multitasking. But when you have to apps open (eg. two browserwindows), windows will handle the tasks by ONE cpu using polling as well (and maybe a few hardware interrupts). (Ok, there's also Dual Processors at the horizon, but they still poll - as long as you don't have a processor for each task)
Uh, I kind of doubt this will answer your question :) but - anyway, maybe it's useful.