I don't see the point of not including male characters just because it's a yuri, it just limits potential stories that can be told.
I would probably have prefered if the guy just saw her as a friend though. While male characters in general seem like a rarity in the genre, I don't think I've ever even read a yuri where a main character had any male friends so it would have been really refreshing.
That said, I highly doubt she'll say yes. Hopefully she'll just let him down quick and easy but she'll probably say that she needs to think it over and figure out her feelings before giving him a proper answer. In any case, I hope they'll stay on good terms.