Tesla had already been granted a subpoena against other companies, such as Apple, Microsoft and Google, earlier in the week. The concern here is that Tripp may have shared proprietary information that could harm the company. Tripp, however, claims he's a whistleblower and was trying to inform the public about safety issues. Specifically, he told Ars Technica that he had seen damaged batteries allowed to ship to be installed in Model 3s.
Tesla, unsurprisingly, vehemently denies Tripp's claim, and it should be noted that whistleblower protections don't apply if the person in question leaks to the media (which is what Tripp did). This lawsuit is notable for many reasons, though, including because of how many other tech firms it's involving through subpoenas over data storage.