Reading a graph left to right from x1 to x2: increasing, decreasing, or constant is always a statement about a specific interval, never the whole graph, and never a complete answer without naming that interval.
Is the graph rising, falling, or staying flat? A function can be increasing, decreasing, or constant — but always over a specific interval, read from left to right.
Saying a function is increasing on that interval is a small, local claim — it says nothing about the rest of the graph. Saying a function is increasing everywhere is a much bigger claim: it means the function rises throughout its entire domain. The two statements are not interchangeable, so say only the one you mean.
Look again at the graph above. To the left of it is falling; to the right of it is rising. Between and it is flat.
What happens outside the interval has no vote on what happens inside it. The falling stretch before and the rising stretch after do not change the fact that the function is constant between them.
"Increasing" on its own is never a complete answer. A complete answer states the behaviour — increasing, decreasing, or constant — and names the exact interval where it occurs.