It was probably a misconception.
But yeah, I strongly believe "Arthur" is going to end sooner than later. I bet there will be a climactic moment occurring on the series finale, and the decision to wrap up production after Season 24 was supposedly pre-determined well in advance. From what it sounds, it implies that the production crew know well in advance that cancellation is coming, and they decided to wrap up the series on their own terms without facing a cancellation notice.
However, if "Sesame Street" were to end the series (likely not for quite a while), that series will likely go out a normal episode, with nothing big happening, and no hinting of the finale.