🔇Does opening a leveraged short on Binance add real market liquidity to the coin, or does it only affect Binance’s internal order book and accounting system?

Short answer :No (just a exchange profit)

When a user opens a leveraged short on Binance, it does NOT directly increase the real on-chain liquidity of that coin.

Most of the time, it is platform-level (internal) liquidity, not real coins being added to the market.