I don't have any inside info but transferring to Newbury Park High School is pretty common for a number of reasons some sports and some academic.
First off Newbury Park isn't its own city but part of the larger city of Thousand Oaks (130,000 residents) and the high school is part of Conejo Valley School District which also serves a few other cities / incorporated areas of Ventura County. The Conejo Valley district has 5 high schools and these are fed by multiple middle schools and students switch schools within the district for a variety of reasons.
Newbury Park High School is one of only two International Baccalaureate programs in Ventura County (population 850,000) so there is a strong academic draw and it is not uncommon for students outside the district (but living in surrounding cities) to apply and attend NP. In addition to academics some other common reasons for Interdistrict Transfer include: childcare i.e. a person may live outside the district but work in the Conejo Valley District. They may want a specialized program offered by NP or the Conejo district, a sibling might attend, their parents might have divorced and one lives in the district or one out, they maybe moving out of district but want to continue their enrollment at the school they were attending, they may actually be moving into the district.
While transferring to Conejo from out of district for athletics isn't an official reason it certainly has happened in the past and as others have mentioned this isn't atypical anytime you have school districts that overlap multiple cities. I live only a few miles from the Conejo district boundary and so we have different schools that serve us but I have a few neighbors whose children attend NP. One did it for track, another did it for the IB program. Other states may be different but in California inter district transfers are pretty common as our school districts are a bit of a hot mess. Some encompass entire cities some include parts of multiple cities and it isn't uncommon for a smaller city to actually be part of three school districts.
I used to live in Saratoga, CA a city of 30,000. It was actually served by 4 different school districts Saratoga Union School District, Campbell Union School District, Cupertino Union School District and Moreland School District. Depending on your street address your child might attend one of the school districts in California and another child living less than a mile away in the same zip code might be assigned a subpar district and attend a school located in a separate city from where they live.
Recruiting athletes from out of district while long disallowed has long been practiced especially for football and basketball.