Calling it 'old-timers' disease' instead of 'Alzheimer's' isn't a mistake — it's a pattern

An eggcorn is what happens when someone mishears an unfamiliar word or phrase and unconsciously replaces it with something that sounds similar and actually makes a kind of sense — like 'old-timers' disease' for Alzheimer's, or 'to the manor born' for 'to the manner born.' Linguists Mark Liberman and Geoffrey Pullum coined the term in 2003 after one such substitution, 'egg corn' for 'acorn.' Unlike a random error, an eggcorn reflects real, if mistaken, reasoning about what a phrase ought to mean.

— Geoffrey Pullum & Mark Liberman, Eggcorn — Coined 2003, Language Log