TV channels that aren't news channels can have news programmes as part of their schedule, in the same way there is ITN News or BBC News.
The name of the channel is a bit misleading but they didn't win Best News Channel, they won Best News Presenter and Best Multi Channel News Programme, for a specific programme I imagine.
It is voted on by viewers, so it is unlikely they have bribed anyone. It could just be they have campaigned more vigorously on their programmes. In the same way Tim & Simon do on Sunday Brunch for another award. Or the way Phil & Holly do (or used to).
They will have to be careful in the run-up to an election as different rules apply. I would expect Ofcom to pay close attention then.