I vaguely paraphrased this from a paperback chess guide of mine (hopefully more credible than the internet). According to my guide, grand masters can effortlessly memorize the positions of realistic matches. But for "nonsensical chess matches" where the positions were randomly generated, the masters were just as bad at recall as the noobs. From this data, my guide inferred that masters rely on recalling attack-patterns from their experience more than brute-force calculation. Similar to how a tourney-strength player has openings memorized by heart, I imagine that a master recognizes common middle-game patterns like the back of his hand.