Question on Scrabble (Dispute Between Hubbie and Myself!)

OK, I've never resorted to asking a forum anything before but I am so sure I am right! So.......a word comes DOWN the scrabble board (GAMED).

Hubbie then puts an O next to the D to make DO and then proceeds to add L and D under the O to make OLD. I am sure you

can't just add letters to a word you've already made. Surely the word DO is his turn? He is convinced it is OK but I am sure it isn't. I hope I've explained it enough, I'll also add a screenshot. Please let me have your thoughts.

Thanks so much :-) xx