Hexadecimal is base 16. A drum loop has 16 steps. Match them up and a hex digit becomes a beat.
How it maps
Each beat slot is one of 16 positions: 0,1,2,…,9,A,B,C,D,E,F. A two-digit hex value 'F0' means hits on the first 4 beats, silence on the rest. '55' alternates every other beat.
Most digital drum machines actually store patterns this way internally. You're not pretending — you're peeking under the hood.