This is part of the game. Here's the relevant bit from the Help tab in game (bold italics me):

"League generation

At the end of day 2, leagues are generated attempting to fit as many friends who are the same level in the same league as possible. Your friends who end up in the same league as you are colored blue in the league table. If there are not enough players to create a league, players from lower levels may be selected to fill the gap; for example, this may result in a level 10 league with 13 clubs with level 10 and 1 club with level 9."