Could be, but not necessarily.
You have two points on the graph: (0, 2) and (2, 4) .
Yes, there's a straight line that could go through those two points. Y = x + 2 .
But there are a million other graphs that could go through the same two points.
You could draw ellipses, parabolas, circles, exponentials etc. that all go through
them. So when you only know two points on the graph, you can't really tell what
the equation has to be, or whether or not it's linear.