Can I Flashbang a D.Va Calling Mech?

1. McCree's Flashbang is a grenade which stuns anyone within the blast radius. Channeled ultimates differently interact with Flashbang hero-by-hero. For example, Whole Hog is cut out when the Roadhog is Flashbanged, while Bastion's Configuration: Tank will not be cancelled (although its duration will be wasted while the Flashbang is active).
2. D.Va, while she lost her mech due to 'dying' once or Self-destructing her mech, can use her "ultimate" Call Mech to re-summon her mech.

Given those premises, here's my question.

1. Can McCree stun D.Va Calling Mech with his Flashbang and cancel it?
2. If the answer for the first question is "yes", will it register for the achievement "Whoa There!", which requires you to shutdown an enemy using their ultimate with a Flashbang?

To answer the first question: yes, the flashbang will stop D. Va from boarding a called MEKA.

Unfortunately, it doesn't actually set her ultimate charge to 0 (she can immediately press 'Q' if she survives the stun), so I don't think it counts for 'Whoa There!'. Not exactly sure, though, since I haven't been in that scenario from McCree's perspective.