If this Lake Indawgyi is the one at 25 08N 96 20E then some (at least) of the following may be deduced.
230 Sqn had a Det at Calcutta (from Malcolm's rafweb), and these Sunderlands were using a FOB "somewhere up the valley of the River Bramaputra". Just how far 'up' may require someone with access to the 230 Sqn ORB to determine.
However, the two statements in the Press Release would seem to be accurate - if put in juxtaposition to create effect (not an unknown media tactic!).
The lake is c. 700 ft AMSL (from GE). There are mountains at 10,000 ft (+!) 200 miles north of the lake (from GE). The normal approach to the lake IS through mountains, but NOT the 10,000 ft mountains - unless operational circumstances dictated the route as being right up the Bramaputra valley and then turn south to approach the lake. In this case the 10,000 ft mountains would have been well within 'navigational error' - and in the mosoon period, with limited navaids, a distinct possibility!!
Having flown as the Met Observer in the Weather Ship 20 mins ahead of a huge stream of Hercs on Paradrop Exercises on a number of occasions in fairly duff weather and having the technical input as to whether the Skipper said "Scatter, Scatter, Scatter" I know how one's sphincter muscle does twitch slightly. And we weren't being shot at!!
Meteorology is a science; good meteorology is an art!
We might not know - but we might know who does!