They didn't say that "it will most likely not happen". They've just said that they won't talk about their projects for NS at the moment.
Yesterday they've released Skyrim SE for PC, PS4 and ONE - A NS announcement would hurt their (Christmas) sales. And that's true because I would buy Skyrim SE instantly for PC but I'll wait for the NS version now.
Another thought: They've shown Skyrim at so many times in the NS trailer, so this is another message than just: "We've 3rd party support." Do your think Bethesda would risk to ruin their reputation? And if they would not plan to bring Skyrim to NS, they would clearly say: "No, it's not coming" because they've nothing of the rumors (On the contrary: The rumors hurt their sales - like my purchase). But they can't negate the rumors because they're true. Skyrim is coming for NS!
It's the same thing when Nintendo has said: "The NX will not supersede the WiiU" (this was end 2015/early 2016) and now they've said: "The Switch will not supersede the 3DS." Do you really belive in this?
We still have 5 months until the Switch comes ...Nintendo would lose billions if they say anything else (same for Bethesda in a smaller frame).