Exactly. 2 very important things happened in 1965 war which helped India in 1971.
The first was that Pakistan left East-Pakistan (now Bangladesh), which formed almost 50% of Pakistans population and landmass, completely unprotected from an Indian attack. This contributed to Bangladeshis disenchantment with Pakistan caused the unrest in East-Pakistan in 1971, which India exploited to the fullest.
The second was the learning that Indian military got in the 1965 war. Indian got to know Pakistans military strategies, strengths and weaknesses which it used to the fullest to its advantage in 1971. The most important lesson learnt was that India could check-mate Pakistan in Western sector. This was important because, Pakistans whole military strategy in East Pakistan was based on the premise that 'defence of East was in the west' i.e. in case of war in East-Pakistan, west-Pakistan would make huge territorial gains in the west Viz. J&K, Punjab and Sindh sectors, that they can negotiate a cession of hostilities with India on its own terms. The 1965 war gave confidence to the Indian military strategists that it can counter Pakistans military strategies to defend its Eastern wing.
So in effect, what Pakistan started in 1965, India ended in 1971, with a complete and emphatic victory.