Not watching the season yet, so no comment on the actual scene in the actual episode, but I do want to chime in re: Liebchen! Because my main association beyond the old-fashioned "lover" you mentioned (positive or negative): older women in the Rhineland/Lower Rhine area, who use it as a pet name for everyone from kids to adults. (Mostly female kids/adults, but it wouldn't particularly surprise me to hear it used for boys as well.) It's probably a regional dialect thing, and definitely comes across as somewhat old-fashioned, but Liebchen as a general pet name is definitely a thing in this area of the country.