That's good to hear. But this is something expected for such an expensive product.
The term “ expensive” is very relative.
AF calibration isn't something new and are often carried out with many lenses by enthusiasts in order to get more accurate output. It is for the same reason higher end cameras come with an 'AF-Fine tune' feature.
Though it costs around Rs. 60k, the Sigma 150-500 is still the cheapest telephoto lens available in the market to get to 500 mm. The other available options are Tamron 150-600 which is about 30k more expensive. The Nikkor [Nikon] is still more expensive. To get this focal length, the budget option from Nikon is the Nikkor 300 mm F4 prime + TC [ 14/17] which should set you back by a bit more than 1 lakh.The latter still doesn’t give you the convenience of a zoom and has no VR as well, but is a superb prime glass with spot on AF accuracy and precision.
If you are a birding enthusiast, 300mm isn't good enough in most situations. The Sigma 150-500 with AF tuned to match your camera body is still a good choice when shooting in moderate to good light.