Yes, fake insiders come and go but these have been right in ways it's not about luck + Nate is just the best Nintendo insider from Resetera and basically works with Nintendo, knows about their first party stuff.
The 3rd party thing again, this might be a more first party Direct focus since they haven't announced any the whole year beside Paper Mario. That statement happened like before the usual E3 time. Means they were probably saying to not hold on to their announcements cause Nintendo were unsure of when they would make a presentation again. It was uncertain time and they just let them know.. doesn't mean they won't do one like several weeks after.. it will be like 2 months after that at that point.
You got that Takahashi thing wrong, they said the Directs might not be a thing that last forever so they are looking in ways to announce stuff. Nintendo are literally the most affective format right now and i'm telling you, and from analysts opinion's as well, they aren't getting rid of this anytime soon. No wonder everyone has a Direct format now. I don't see them announcing their whole lineup for the rest of the year on Twitter.