There's a literal, specific, legal difference between a split and a stock dividend.
In a split there's no impact on short holders at all.
When a dividend is issues, the short is required to provide the same thing the lender would've gotten as a dividend to that lender.
Respectfully, I don't think you're correct, and by being so certain, you are misleading a bunch of shareholders.
I believe what you're describing applies if Tesla issues a stock dividend by diluting current shares similar to how they would issue stock compensation to employees. This is not what's happening. It is indeed a stock split where the number of shares increases 5x, but each share is worth 1/5.
The shareholder who is lending out shares has entrusted their shares to their broker. The broker is obligated to return the shares
at any time the shareholder decides to sell. A stock split is immaterial to this obligation because the position value does not change.
Example:
Shareholder A owns 1 share of TSLA and joins the share lending program at Broker B to allow their share to be lent out.
Broker B takes the 1 share and lends it to Shortseller C.
The share is sold short to Shareholder D from another broker.
Shortseller C pays 0.5% interest to Broker B.
Broker B pays 0.25% interest to Shareholder A.
Stock split dividend happens.
Now Shareholder A is entitled to 5 shares which is trading at a new price of $300.
What does Broker B do?
Force Shortseller C to close 4 shares so both Broker B and Shareholder A stops earning interest?
What is Broker B going to do with those 4 shares? Wave them in front of Shareholder A and tell them they'll stop earning interest on them? No, Shareholder A has already agreed to lend out their position. Because this does not increase risk for the broker, they will continue to borrow the 5 shares from Shareholder A and lend it out to Shortseller C unless Shareholder A decides to call back (sell) their shares at any time.