Since the entire effect of A Wingbeat of Giant Dragon happens during resolution, the controller of the effect must be able to return a Level 5 or higher Dragon-Type monster from the field to the hand during resolution of the effect. A face-down monster's Level and Type cannot be determined, so it cannot be returned for the effect. Without returning an appropriate monster, the effect of A Wingbeat of Giant Dragon cannot continue to resolve as the conjunction "and if you do" is used, so the effect of A Wingbeat of Giant Dragon resolves without effect.
These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official and can still be correct, as long as they follow the official gameplay rules, or unless Konami has issued a ruling that says otherwise. References: 
↑Konami Judge Program Rulings are considered unverified, as their source(s) are not publicly viewable. They are not confirmed as applicable to the TCG until they have been officially published by Konami.
↑Konami OCG Card Database: If "DNA Surgery" is treating all monsters as Dragon-Type, you control an "Archlord Kristya" treated as a Dragon-Type monster, and you activate "A Wingbeat of Giant Dragon" choosing "Archlord Kristya", since "Archlord Kristya" returns to the top of the Deck by its own effect instead of returning to the hand, is the effect that destroys all cards in both Spell & Trap Card Zones still applied?
↑Konami OCG Card Database: If you only control a "Horus the Black Flame Dragon LV6" that is unaffected by Spell Cards, can you activate "A Wingbeat of Giant Dragon"?
↑Konami OCG Card Database: Can a Fusion, Synchro or Xyz Monster be chosen by "A Wingbeat of Giant Dragon" effect? Also, if they can be chosen and the monster isn't returned to the hand, is the effect that destroys all cards in both Spell & Trap Card Zones still applied?