This doesn't mean the DOJ expects to find wrongdoing. The review is largely intended to reexamine tech companies' dominance in light of evolving market conditions. It comes just days after a reported plan for a multi-state antitrust investigation, though, and it may not be so fortunate on that front.
There's simultaneously little doubt that Google is anxious about potential regulatory action. It opened its response to the DOJ inquiry by claiming that Google services "create more choice," support "thousands" of jobs and businesses and pouring money into research projects that "spur innovation." Google knows that officials could demand drastic changes (such as undoing acquisitions and splitting up the company), and it wants to dissuade those attempts by portraying itself as an essential part of American society.