Battle of Peshawar was fought between Mahmud Ghazni and

the Battle of Peshawar was fought between Mahmud of Ghazni and Avtar Dev, and that Avtar Dev defeated Mahmud of Ghazni with the combined strength of all Jammu hill chiefs" is historically inaccurate based on widely accepted historical records.
The Battle of Peshawar (1001 AD) was fought between Mahmud of Ghazni and Jayapala, the ruler of the Hindu Shahi dynasty (not Avtar Dev). Jayapala was defeated, captured, and later released after paying a large ransom
There is no credible historical source that mentions Avtar Dev fighting or defeating Mahmud of Ghazni, nor is there a record of the Jammu hill chiefs uniting to defeat Mahmud.