no surprise.... its common practice in global aviation scenario. As is said already... its probably due to an earlier buy back negotiation Boeing conducted with any of its customers who were earlier operating Airbus aircrafts but for n number of reasons and specific contractual details or fleet utilisation/optimisation/feedback wise they decided that ordering and operating aircrafts from Boeing would be better than their existing Airbus fleet. In bargain Boeing would reduce the price factor for their aircraft in exchange for the Airbus aircrafts of the customer.
much like a car exchange scheme... Boeing Lease Corp/Financial etc would take the Airbus aircrafts from the customer and in return provide them with new or other inventory Boeing aircrafts at a reduced price. Later the Airbus acquired in such a fashion are then put out back on sale/lease to airlines that would have a requirement for them.
just to cite and example : Singapore Airlines operated Airbus A340-300s which they phased out in favour of the 777-200ERs while the A343s were still pretty good. Was back in 2005 if i remember correctly... Boeing agreed to remarket the 17odd A343s as part of the deal.... at that time SIA had still to take delivery of a few A343s from Airbus even!! and they already decided to phase them out!
as DABTH mentioned.Like a Car Exchange deal.Boeing wants to sell their Aircraft to an Operator that currently owns a different Manufacturers Aircraft.So an offer to Buy back that Aircraft in Exchange for a Boeing product at a discount will be made.
Now Boeing has to get rid of these Aircraft.Hence the offer.
Imagine DN doing DEL-BOM on those a/c they'll have a full load of 300+ pax in one lift which can be a turning point in Indian aviation. Don't know if you remember what JAL did with the 747's flying them domestically from Osaka, Tokyo and Nagoya.
JAL flew with the 747-400D... a subtype of the regular B744 with strengthened undercarriage and wingroot in addition to enhanced structural rigidity allowing for greater cycles and number of T/O and landings..
most noticeable difference compared to regular 744s was the absence of the winglets and subtle changes to wingroot.
almost resembled the 743s... especially the later versions of the 743 which featured 744 type wingroots..
JAL operated them in high density configs of 500+seats if im not mistaken