No, this point show an angle x which its sine is 4/5; that is sin(x)=4/5 and by the reflection about x-axis x becomes -x and then you have sin(-x)=-4/5.
Here is what I wrote:
"Sine is an odd function because whenever it passes under the x-axis, it becomes negative.
A 3-4-5 (point (3,4) on a circle) triangle in the first quadrant would have a sine value of sin(4/5). If the triangle were reflected over the x-axis, the sine value would change to sin(-4/5).
Another rationale why sine is negative is because it has no symmetry over the x or y axis. Cosine is symmetric over the y-axis, thus it is even. "