Yeah, by the standards of the time it was an extremely warm winter nationally and still the warmest on record for the city of Chicago. The strong Niño signal was definitely there, even way back then.
Our early January cold that year is another strong Niño trademark. It's not mentioned very often but there is a very strong correlation with cold here in the December 20-January 15 timeframe with stronger El Niños. Actually one of the best ENSO-cold correlations we have in our region (most recent example being January 2024). Could be worse!