^Recall that the Romulans of TOS were much more Federation-friendly than their TNG counterparts. It's not entirely implausible that a Romulan diplomat would be present for such a meeting. Were Smilie and the others concerned about his presence being a security risk, they could simply have asked him to leave.
--Sran
Right. Remember the Romulans go into a period of focusing on their internal matters and basically disappear from the Alpha Quadrant political landscape sometime after the TOS movies and stay that way until TNG "The Neutral Zone". But before this it seems that they were more present in politics. And of course started to become much more present diplomatically again with the Dominon threat on the other side of the TNG-era. So when big quadrant affecting events happen it does seem like they're interested.
Given the Romulan dislike for Klingons (and vice-versa), and the even bigger threat an alliance between Klingons and the Federation would pose to their empire, you can certainly see why they'd want it derailed. Which they try to do again in the TNG-era throughout Season 4.