The ghost movement is not random. They go in memorizable patterns. So it is possible to simply rote memorize the solution to all 256 levels or something.

Back in the day it was combination of being young and paying attention to the basic patterns of the ghosts, then keeping a count of dots eaten so you could know when fruit was going to appear.

Each ghost has a set behavior in each phase of a board, plus a different way of picking where to go. The red ghost is always trying to get to where you are, but pinky is trying to get ahead of you. I can't remember all of it any more, it's been over thirty years.

Back then, it was all a bunch of kids spamming quarters and figuring things out as best we could. I wasn't the one to figure out the patterns, I was just good at using them. And my hand/eye coordination was fast. So I could see the ghosts and where they were going, then adjust my movement before it would be a problem.

Staying ahead of the "ai" of the ghosts was the only real way to get past around lvl 50. Before that, you could usually just clear a quarter of the screen while avoiding them reactively. After that, if you weren't able to visually track all 4, and have a sense of where they were going to be, you'd eventually crap out, or lose fruit, which means a lower score.

There's articles out there now that give details I had no idea were part of it back in the arcade days though.