Benjy had shared with Gideon the basics of what was going down, but he would let Tonks fill him in on the rest of it. She was more in the know about everything, anyway, so she was definitely more qualified to do the telling. The most important thing Benjy had shared was for Gideon to be in the reading room at 4pm. And right at 4pm, Benjy was there and ready for this little meeting.
Since it appeared he was the first one to arrive, he made sure to look as inconspicuous as possible while he waited for however long it took for either Tonks or Gideon to arrive. So Benjy busied himself looking through the books on the shelves and even went as far as selecting one to read. He doubted he'd finish it, or even get very far at all, but he could at least pretend to read it for the moment.
He'd just sat down when he saw someone walk in. Not knowing exactly what Tonks looked like, let alone that she could change her appearance at will, he eyed the newcomer warily and pretended to read his book. They really should've come up with a code or something so they'd know who was who.