The article seems to say he put on 15 pounds of muscle in one month:
Stuck in an apartment in St. Petersburg by himself for a month waiting to get over his case of COVID-19 and get the requisite negative tests to rejoin his teammates, new Rays outfielder Randy Arozarena figured he would make the best of it.
He taught himself to cook, improving his usual diet with a healthy version of chicken and rice, and stuck to a regular exercise routine, including 300 pushups a day, putting on about 15 pounds of muscle.
MLB:
During quarantine at an apartment in St. Petersburg, Arozarena learned how to cook. All he knew how to make was chicken and rice, so that’s what he ate almost every day. He paired that with nearly 300 pushups a day and reported to the alternate training site in Port Charlotte, Fla., with almost 15 added pounds of muscle.