To answer your question, first let’s see how the Hindu mother has acquired the property and how she passed that onto her son.
Property of Hindu Females can be divided into 3 types:
(a) property acquired by husband or father-in-law
(b) property inherited by father or mother
(c) property received via gift or will or any other instrument or her self-acquired property.
So, as per your question the mother acquired it through both (a) and (b).
Section 15 of the Hindu Succession Act, 1956 states that any or all types of above mentioned property will pass on to her children or great grandchildren or any such other legal heirs (as according to rules and preference given under Section 16 of the Hindu Succession Act, 1956).
Consequently, as per given question the son of such Hindu mother inherited those properties according to the above stated provisions.
As a result, the property received by the son would not be considered as ancestral property, since property inherited from one’s mother, grandmother, uncle, brother, or any other relatives is not certified to be an ancestral property.
Ancestral property is said to be property inherited from father, father’s father, or great grandfather only; as reiterated in Gurdip Kaur v. Ghamand Singh SCC 180.
Thus, the property received by son will be self-acquired. As he also eventually died interstate, according to the provisions of the Hindu Succession Act, 1956; the self-acquired property will devolve upon his children as they are included in Class I heirs and the children shall retain the property as self-acquired as well.