With the last panel showing a classroom scene we've never seen before of Katou holding a piece of paper and Yui by the door, I'm assuming that was a drawing that Yui made and Katou found, which led to them interacting for the first time, and that's why she initially choked up and asked "which one" when Yui brought up seeing a framed drawing. Or I could just be completely wrong
actually, you might be onto something. I saw Yui saying "Red Pin's" and just auto-filled the rest of it, but given she talks about "print[ing] about 3 copies from the data [he] gave",
and the flashback in the final panel of the chapter, her having framed something he drew would make sense. Plus, he calls it a 'drawing' outright. Not "a print" or anything like that.
And it would mesh with his surprise in the previous chapter upon laying eyes on whatever was in the frame. Thinking about it more...I don't know why he'd be necessarily surprised at Katou framing that Art Pull he'd gotten and then gave to her. Sure, she was super about it, but his reaction at the end of ch.8 doesn't line up, to me. Something he drew, and she found/received from him,
would garner that response, and would be significant in his estimation of how she feels about him. (Yes, she "sidestepped" admitting to anything deeper in her Otaku Blabbing at the end there, but the point stands).
So either way I'm now subscribing to your hypothesis.