I had forgotten the business card plan, so I wasn't sure what he was going to tell her, but it most certainly wasn't going to be a confession. It's interesting that despite knowing better logically, Shibuya simply couldn't help but convince herself of it being a confession of all things. That alone should make her realise her own feelings (which the story didn't foreshadow all too well).
Since she knows Akiba is that sort of "herbivore" guy, why not go after him? Oh, right, the chapter ending already stated why not: if they become lovers, they aren't friends anymore. Normally you'd think that's an upgrade and not worry about it. Instead of such nonsense, she should instead try to ponder if Akiba could mentally accept it. They have grown decently close, but it's still almost 100% related to cosplaying. So, while's comfortable in her company as long as cosplay (and the club) is somehow involved, would he be comfortable as her boyfriend? There could be grave self-confidence issues involved on his side, even if we know he does actually like her a lot.