OK , just read Cricinfo. Let's try to see it bit differently.
- BD had 6.06 asking rate at start of their innings.
- Rain came around 14 over mark. So with 6 an over , SL should have scored 84 runs.
- Target was revised for 183 runs in 27 overs. 13 overs were left.
If BD was just scoring around Required rate then they would have been around 84 runs and 100 more runs left to reach 183 target. So effectively, BD was told to score 100 runs in 13 overs at 7.7 runs an over.
So in short, BD had 50 overs game in start with required run rate of 6.06. Assuming, BD was just matching the RR for the first 14 overs and rain come. They were suddenly given next 13 overs with 7.7 required rate.
Others have pointed out, it doesn't take account of quality. It seems true but quantitatively, BD got revised target of 7.7 asking rate. That's seems big adjustment to me. If BD had batted very slowly then asking rate would have been closer to 9-10, so credit to them to bat at much faster rate than required rate for the first 14 overs. That's why they had easier time after the rain and adjustment looked less daunting.