Musk had recently said that Tesla was "single-digit weeks" away from the crash in 2017, as he focused all the company's money into increasing the production of the Model 3 sedan. Tesla finally survived, and has since rolled out the Model Y SUV and unveiled new vehicles like the Cybertruck.
Apple did not respond immediately to a request for feedback.
Apple has spent the last half-decade toying with the entry of hybrid and self-driving vehicles into the country, but before this week it was believed to be focused on designing applications and other technology that could be marketed to other businesses. But on Monday, Reuters announced that the Silicon Valley giant had re-engineered its focus on creating a hybrid, autonomous vehicle for general customers.
One of the reasons Apple has reportedly changed course again is that it has made strides on a possible battery breakthrough.
According to Reuters, Apple has been designing a lithium-iron phosphate battery that can be packed more closely in the car's battery pack, minimizing weight while increasing the possible energy density.
On Tuesday, Musk found out on Twitter that Tesla is still using iron phosphate batteries in some of the cars it's producing in China.
"Strange, if it is true," he wrote.
Tesla and Apple have traded a lot of talent over the last decade. When the stories of the "Apple Car" first appeared in 2015, Musk joked that Apple was a "Tesla Cemetery."
If you're not doing that at Tesla, you're going to work at Apple. I'm not kidding, he said.
Musk said at the time that the electric car was the next logical thing for Cook and Apple to focus on.
It's a positive thing that Apple is moving and spending in this direction. But vehicles are very complicated relative to mobile or smartwatches, said Musk.