Supremacy-The Great Game tradition has a hidden bonus?

[moyang]

It gives the old unity bonus from neighboring rivals.
I suspect this is a bug...

tr_supremacy_great_game = {
    possible = {
        has_tradition = tr_supremacy_overwhelming_force
    }

    modifier = {
        shipclass_starbase_damage_mult = 0.20
        starbase_upgrade_cost_mult = -0.33
    }
  
    #implementation in the "should_apply_neighbor_rival_modifier" game rule
  
    ai_weight = {
        factor = 1000
    }
}