A function does not have to be a continuous line. Unless the directions told you it is a line, it can be a list of points, or it could be a line, or it could be a parabola, or it could be a curve. As long as no two points in the function have the same x coordinates, it is a function.
Since there are so many options, it is not possible to answer this question accurately. We don't know if it has one root since no value in the table shows y = 0. If the function is not continuous, it may have no point where y = 0, so there are no roots. If the function is continuous, then it has AT LEAST one root between -2 and 0 since the y values go from negative to positive. It is possible this is part of a parabola. If that is the case, then there would be a curve at some point that creates another x intercept. It might be a higher order function with multiple turns that create more x intercepts.