5.3% is not incredibly low for a corporation borrowing 1.8 billion. it is pretty high which is why investors are jumping on it.
This adds $95 million in interest expense per year which is pretty substantial.
It is incredibly low for bonds in the "junk" trough. For companies with Tesla's credit rating, you're typically looking at 6.5-7.8%. If you're GE, you're of course going to pay a lot less, but GE has a much more robust credit history.