1.03 seems waay too low. There is no way AJ wins that hard. They are both huge dudes anyways, as you said ruiz has never been ko'd so it makes no sense to think that it will happen this time with that certainty. Even 1.25 seems bad to me. Ill probably bet on other stats.
That's merely 3% return of your money and it seems that is a sure win since i think Joshua won't lose this fight. Ruiz is just a replacement fighter though not a pushover but still he got no chance against Joshua.