Well we should all be level headed, Its true India will find it difficult to export sophisticated weapons to Vietnam or any other country for that matter that are 100% Indian, without Russia(or Israel/West) being a part of it/JV etc. So this makes it quite difficult for India to supply weapons to friendly countries and further its interests. This complicates matter for India, since in this case the only weapons it can sell that are really 100% Indian made, it needs to give offer concessional loans/gifts/grants for these countries to even think of purchasing them(mainly because they have better options). This makes it more difficult because countries like Vietnam have better options like Russia from which most of Indian weapons are derived/produced under JV, so most countries like Vietnam will rather purchase them directly from Russia/ukraine etc.
In this case, India has to prioritize its own national defence industries, at all cost. Since this will not only provide India with the necessary know how/Knowledge but will also help boost its economy, since a large defence industry/military complex has several spin offs to other sectors of the economy. So this will have a multiplier effects of helping India Boosts its economy/defence industry and help it further its international influence/interests by exporting such arms to friendly countries, thereby solidifying itself has a credible world power in its own rights(without depending on others) like the U.S,Russia, U.K, France, China and Germany are doing today.
Im sure with proper planning/vision and determination, India can achieve this in the coming decades.
As for this deal, its good for Vietnam, since it has nothing much to lose, but everything to gain in such a loan/credit for acquiring some defence equipments to add to its inventory. Though its not really a big defence deal like the one Vietnam often signs with Russia and other countries. But still a good start.