@BernyJB
Based on what you have written, I am pretty sure that you are getting the gist of what "short selling is".
Scenario 1 pretty much sums up the concept of Short Selling, but with the addition of what we call the "
Margin," which raises the question of how a person who has an open short position and his trade goes south will be able to buy back that particular financial instrument for more money than what is in his account because he simply borrowed it in an exchange. This is where the
initial margin comes in, which acts as collateral to ensure that you really can afford to buy the crypto/stock back in the future. This collateral, however, is vulnerable to a process known as "margin call," in which your collateral is emptied if your account cannot handle any further losses (the prices keeps going up).
In other words, you need to have an initial margin of BTC(or any other crypto) or Stablecoin(e.g., USDT, BUSD) for you to be able to open a short position especially in Futures or Margin Trading. I would recommend that in order for your understand this further, you need to at least try a 1 dollar trade in Perpetual Swaps Futures while closely monitoring your PnL, Initial Margin, and your overall capital to see a concrete example for yourself.
scenario #2 is not short selling
I would assume that you are talking about shorting in Spot Trading and not in Futures/Margin Trading here. Selling at a higher price and buying back at a lower price even without having an initial margin can still be considered as "Shorting" in a traditional market like Spot Trading because you are still
covering your short to be able gain back your initial capital plus the extras which you have gained for buying back at a lower price which is your profit.