You flopped a straight. I don't like giving a free card to a super draw heavy board. Very easy for two pair, four card straight, flush draw to catch up to you. I also don't see how you were able to discern that nobody had KQ. If someone bet weak then they could be slowplaying the nuts especially if they have the Diamond redraw. If someone bets strong they could be making a semi-bluff with the nut flush draw possibly with a straight draw to go with it.
Its hard to say, sometimes I just know. The only thing I can really credit such feelings to is my experience, I've played in the same games against the same sort of players virtually everyday for around 4 months, so I think when I'm focussed I can have a good feel of my table, and how my opponets will play in certain spots.
Although your perfectly right someone could slow play KQ, it just didn't feel like it here, against other players or in another game I may have got a totally different feeling or had no idea at all, but here I felt there wasn't a KQ out there and my reads are right often enough in these games that I tend to back them up with my chips.