Not exactly, while it is very likely that
@nvr2old will get their Storm Trooper bucket for their son. There is no guaranteed inventory, the collectible buckets are sold "While supplies last" via walk-up and Mobile Order.
Guests also make walk-up purchases as well as Mobile Orders all day long. And I have had a CM that insisted to verify my mobile order receipt when picking up my order for 2 Dole Whips.

...
That appears to be part of the new "Live" activities update for Mobile Order tracking as of last week that is currently only available on iOS .
You get a Push notification and you just reply with the "I am here" right from the smartphone lock screen notification. You don't to open
MDE, and then select your mobile order to select the "I am here" button.
Dave