You did get the background right. At 500mm with the background some way behind the Robin, the blur from a wide aperture will usually guarantee this.
You have the comment above about shutter speed. I have looked at 6 or so of your previous bird shots where you have used 500mm. and in every case, the bird is not sharp, and, the shutter speed is very slow.
The exif data is not identifying the lens, - I assume its Sigma? If it is, the lens does have Optical Stabilisation. According to Sigma, the OS will allow the lens to be used at 3 to 4 stops under the shutter speed that would be needed if there was no OS, when hand-held.
So lets take a look at what that means. First, OS works to stabilize you and the camera; it does not have any stabilising effect on a moving subkect; movement can still blur.
Next, what does 3 to 4 stops mean? You are using an APS-C Canon Camera, which has a crop ratio of 1.6. This means the 500mm is effectively a 500 X 1.6 lens, or 800mm.
To hand-hold an 800mm lens would normally require a shutter speed of 1/800th; normally assumes the ability to hold the camera and lens steady.
Each stop, as far as shutter speed goes, represents either double, or half any given speed, depending on whether we are taking about less, or more light allowed into the sensor.
With OS, we are always talking about slower speeds than "normal", which are needed to allow MORE light in in poor light situations.
Starting at 1/800, one stop slower = 1/400, two stops = 1/200, three stops = 1/100, and four stops = 1/50th. All this still assumes that you are holding the lens quite steady; and, I would imagine that four stops could be achieved quite rarely.
So, you are at the four stop mark here with this shot. I would suggest that 1/125th would be the slowest that might get you a sharper image.
To get there using Aperture priority, wide open ( its f/6.3 thats the widest for this lens) this mean using ISO 1600.
If you want to keep the ISO at 800, you have to use a shorter zoom. Using 300mm on this camera, which will be effectively 30 X 1.6 = 480mm, would allow 1/60 at three stops, and ISO 800.
Lets say, as an example that you are the worlds steadiest lens handler, and that 4 stops is astounding on the lens. Then you can run into another problem area IF you crop the image tight, - which you may have done here. Close cropping will reveal noise, and the slightest lack of sharpness quite readily, so an overall softer image than you wanted.
So, in summary either higher ISO to maintain 1/125th at 500mm; OR use a shorter zoom; AND dont crop so tight.
I uploaded a mod that has some sharpening (the Robin does not respond much, indicating the original is not sharp); some noise reduction for the background, and a crop that places the Robin off centre and higher.
Hope this helps, and if you have any questions, just ask.