If you think about it from a strategic perspective, this announcement is not meant to discourage delivery of Leopard 2 or its ammo, which is a done deal. It might be meant to justify the use of tactical nukes as soon as Leopard 2 tanks are on the battlefield. Russia knows it cannot win a conventional war against NATO.
If I were Boris I would rather lose a conventional war than lose a nuclear war, but to each their own.