Does "an attacking creature" count as "a creature that attacked"?
The Hypersonic Dragon will be untapped.
It is well established that to attack is to declare as an attacker, so a creature that attacked is one that has been declared as an attacker earlier in the current turn.

508.2. Second, any abilities that triggered on attackers being declared go on the stack. (See rule 603, “Handling Triggered Abilities.”)
508.2a Abilities that trigger on a creature attacking trigger only at the point the creature is declared as an attacker. They will not trigger if a creature attacks and then that creature’s characteristics change to match the ability’s trigger condition

The rule and ruling for &quot;put on the battlefield attacking&quot; further supports this:

508.4. If a creature is put onto the battlefield attacking, [...]. Such creatures are “attacking” but, for the purposes of trigger events and effects, they never “attacked.”
2011-9-22 Although the token is attacking, it was never declared as an attacking creature (for purposes of abilities that trigger whenever a creature attacks, for example).