Whether they could be called missiles is less clear.
The original sense of the word "missile" was "something that can be thrown" (e.g. javelins or arrows).
Balloons cannot really be thrown.
Nevertheless, sometimes "missile" had been used in a wider sense, as "something that can be sent away". In this loose sense the word could have been applied to these balloons.
Whether they could be called missiles is less clear.
The original sense of the word "missile" was "something that can be thrown" (e.g. javelins or arrows).
Balloons cannot really be thrown.
Nevertheless, sometimes "missile" had been used in a wider sense, as "something that can be sent away". In this loose sense the word could have been applied to these balloons.