That small detail is easily missable, don't blame you for not noticing it (neither did I when I read it).
Now, for those who want to figure it out themselves, here's another hint:
The one who picked it up has a different sleeve compared to those two maids.
For those who want another hint:
That sleeve looks exactly like the sleeve of the typical Valkyrie Maid uniform (typical look) (this chapter's sleeve).
And for those who don't care and just want the answer, here it is (with proof):
It was our lovable dumbass who picked it up, a.k.a. Zepto.
As stated above, the sleeve is that of a uniform, and Zepto happens to be one of the maids who has such sleeves (Zepto's sleeve). Zepto is known (or at least hinted by Emily) to be no good in any role that isn't being a Valkyrie Maid (Emily's comment) and had the counter-measure division actually been dissolved, he would have been out of a "job." Since Emily stated that they don't know for sure whether the threat has been eliminated or not, this dissolution did not happen (dissolution). Now given the fact that the Valkyrie Maids don't have any targets to actively pursue, they must have been tasked with observing everything in case something happens. Since Kotomi is pretty much the target of the mastermind, observing him is an absolute must. So who else but Zepto is the most suited to perform this task?
And additionally, the 'person' who picked up the tissue packet is using a rather informal tone (even in the raws), so I decided to have them use "ya" instead of "you" to indicate that ("ya dropped this"); which is how Zepto usually talks.