The button/link in question ("Book Now") is a custom asp:LinkButton control declared in the ItemTemplate of a GridTemplateColumn. As this button is not a built-in part of the Telerik RadGrid but a custom element in a Template, its accessibility compliance is supposed to be handled by the developer like any other configuration in the Template field.
In case a similar structure is needed for a custom application, you can replace the asp:LinkButton with an asp:Button, or Telerik RadButton, or manipulate the aria-role attribute of the rendered element with some custom code.
We are currently in the process of improving RadGrid's Accessibility compliance and such feedback could prove really helpful for us. Please do not hesitate to let us know if you face any issues in terms of accessibility with the default structure of RadGrid.