This link you're providing points to a different Lichess account, other than the one used in the tournament. Notice that I can create a Lichess account by the name of Vladimir Dobrov and pretend I'm him.

So, how can we know that these two accounts belong to the same player?

In case you're new to Hive, notice that in this social network bad practices such as identity theft are common and it's a problem the whole community is dealing with. That's why you're often asked to create an introduction post and provide further information to back up your claims.