The take home message is that, no, he did not deny Nalu. What he DID deny is that he's going to get implicitly romantic with them in the main storyline. If memory serves, it's pretty similar to what I said recently about how the ships have different portrayals and different means to happen.
Ships with mains do commonly have the platonic build with the ending where they get together without the ooey-gooey romance since, main characters tend to be archetypes that appeal to typical shounen readers (young males). Typical shounen readers do not give a rats fanny about the romantic build-up, but they do appreciate a happy ending where the dude gets the girl. Of course, Nalu is deeper than that, but as they are the main characters, Mashima probably treads a fine line on how far he can go between making it palatable to readers and turning it shoujo. The best thing about shipping the mains is that you get a lot of interaction. The worst thing is, you are constrained by plot and often are relegated to canon near the end.
As he stated recently, he wants to play with romance though. He's been a mangaka long enough and knows his wide fanbase enough to experiment. He's been making it clear that he's going that route. It should be interesting to see the end result.