I'm going to overthink this chapter for a bit; Using the Twin Trick here is great because we the readers aren't the only one's disappointed in it. MC is also obviously kinda bored by the entire thing, and Childhood Friend Girl is definitely frustrated that her reasonable deduction was wrong in favor of a 'trick' that she basically had no way of piecing together from the information available to her.
But of course Twin produced a lame answer. She's not the mystery nerd that Yuriko is. Yuriko probably would have come up with a trick more like what CFG or MC's initial misdirection trick, because they are tricks that an observer could deduce based on observed evidence, and don't require outside knowledge to uncover. In other words the best sort of mysteries for a mystery novel.
And yet at the same time it is something we the reader could figure out based on knowing about Yuriko's Twin and how bored and disinterested Toiri is. Because his crush isn't involved he just kinda doesn't care, and ends up treating 'Yuriko' more like how he treats his Childhood Friend this chapter, hinting that something is off about the situation.
Elementary my dear Nerdsons.