Just the one statement Allen makes her explains a whole lot to Alice. After all, it narrows down the events that Allen could have seen by a lot. Especially since she's pretty sure it must have been one of the men she knew in London, rather than in Wonderland. No matter how irritating Alice finds certain Wonderland residents, she doubts that Allen would get similarly irritated enough at them to say that.

So if it's men she knew in London, then.. well, there's only two it could be, right? Most likely Bumby, though it could be Radcliffe, since he didn't exactly always treat her kindly either.

"What did you see..?" Alice therefore asks, wanting just a bit more clarity before she says anything else.

Even with his memory still humming in the back of her mind - but she keeps it there for now, just so she can address it later as well.