What is the meaning of inferred absolute zero temperature? Why does the resistance temperature graph it is obtained from behave that way?
I think you are making much ado about nothing. As stated in the website, they are approximating the behavior of the device with a straight line to make it easier to convert resistance into temperature. As a result, there is an error at the extremes of temperature because the actual resistance vs temperature departs from the straight line. They show that the approximation has an error when carried out to absolute zero which is expected since it is only an approximation. They use the word &quot;infer&quot; because they are using an approximation beyond its useful range.  This is often done with a variety of sensors which behave linearly over only a portion of their range and there is nothing mysterious about it. As to why not all sensors are not linear is a subject for physics, not engineering.