I don't believe so. It appears it's about mixing liquid, full-strength wine with water. https://en.wikipedia.org/wiki/Culture_of_ancient_Rome#Food
I really appreciate you leaving a report. Those reports help improve and shape the course. However, I'm sad to say that when you're marked wrong for typing exactly the correct translation, all that happens is that the admin interface shows a report for a correct translation, and contributors can do nothing but remove it. It's a bug in the system which I really dislike. :(
Why is "They are blending wine and water" wrong?
blend (verb): To mix or combine together http://dictionary.cambridge.org/dictionary/english/blend