Is it so surprising that he wouldn't have been considered mentally ill, especially at the time? Imagine someone who's generally affable, who can more or less hold down a job, who speaks in complete sentences, obeys the usual social rules about manners, dress, and speech --- an ordinary guy --- except that he has a habit of eating a variety of unusual objects. Would you consider him eccentric or would you go straight to mental illness?

I think we're too eager to medicalize personality quirks nowadays. Traditionally, a mental illness is a set of behaviors or beliefs that impair one's general functioning in society. Mere weirdness doesn't count.