Biases are irrelevant. If you look a the numbers, there are more people saying they voted for the opposition on the Telegram pool than votes on the official pool. About 5 times as many.
Also what about all the babushkas who most likely voted for Lukashenko but don't have a smartphone?
This is not to say that more people didn't vote for the opposition than the official numbers state. But Lukashenko still could have won.
There are many ways that could happen. But it's pretty good evidence to add to the context, and the pile of evidence was already quite big.