It’s a valid method that avoids some edge cases where Excel’s autocomplete gets confused. He just forgot the last step of copy and then paste back into the same cells as text to remove the formula.

My pet peeve is my coworker who finds it easier to write macros to analyze the data instead of setting up formulas, and then I am completely unable to follow his analysis logic because it’s all just columns of numbers with no way to tell what was used to calculate what.