C1 doesnt mean its the top team of GROUP C.. The first two teams in each group are placed 1 or 2. They will retain this position for the Super Eights stage, irrespective of whether they finish first or second in their group, unless they are knocked out by team in their group. In this instance, team 3 replaces the position of the team they knocked out.
This is how ICC labeled the top two teams in each group before they started the tournament....
Group A - South Africa(A1) West Indies(A2)
Group B - Australia(B1) England(B2)
Group C - New Zealand(C1) Sri Lanka(C2)
Group D - Pakistan(D1) India(D2)
Because Windies got knocked out in the first round Bangladeshis captured A2 Place..
Super 8s..
Group E - A1 B2 C1 D2
Group F - A2 B1 C2 D1
Semi Finals
The teams finishing first and second in groups E and F, based on points obtained in the Super Eights stage, will compete in the semi-finals.