Nope. Movie was about Thanos collecting the stones and then using them to wipe off half the universe. All of that happened in THIS movie. How is the ending a cliffhanger? It would have been one had it cut to black after he snapped his fingers but sorry, I don't think you "probably" understand what that word means better than I do.
Yea I agree. I think people are looking at it from the perspective of having the avengers be the protagonist as they have been in the first two avengers films. But that's not what the directors and writers intended for infinity war. They've reiterated that Thanos is the protagonist and that it is his movie. So if you look at it from that perspective, he's the twisted hero of this story, he accomplishes what he set out to do, and the avengers look to be defeated. The story can end here and it would be fine, although dark, especially since this is all from Thanos' perspective. This is why it shouldn't be considered a cliffhanger.
Although we know there is an avengers 4, and that the avengers will likely try to fight back against Thanos and undo what he did in this film, that shouldn't change what this film was. The only thing that I can think of that supports this film having a cliffhanger is the whole Dr. Strange plan, since we haven't seen the supposed fulfillment of that plan. If there even is one.