By most senses of the term yes. But there were things that functioned sort of like journals earlier. For example, Marin Mersenne in the early part of the 1600s functioned as a sort of clearing house for math. He corresponded with a large number of people and reported to different people what results others were up to. There were others who acted similarly. But, yes the idea of a regular journal is post-enlightenment. This if anything makes Eliezer's portrayal of wizarding culture more problematic, not less so.