The short answer is no, Xfinity Mobile is not owned by Verizon. However, the companies do operate under the same corporate umbrella.
Xfinity Mobile is a subsidiary of Comcast, one of the largest cable providers in the United States. Verizon also owns a small minority stake in the company.
Despite the lack of ownership, the companies have been working together closely. For example, Xfinity Mobile offers Verizon Wireless customers access to its mobile network.
Additionally, Verizon has been using Xfinity Mobile data to improve its own network. This cooperation is likely to continue, as Verizon and Comcast are both looking to increase their subscriber bases.