In this case the original author was an employee of Google and is not the current maintainer.
Google then released their implementation under the BSD. It was forked and worked on, and eventually it now comes to the maintainer. Had GPL been used at any point the current maintainer would not own full copyright and thus not have legal grounds to distribute binaries without source.
Original authors can only unilaterally change licenses if they were the sole authors, or with agreement of all other authors. Or with copyright assignment contracts as you see in GNU projects.
My comment is also not about the maintainer. My comment is about how BSD as a license is often framed as an equivalent choice to GPL or other copyleft licenses.
Years ago this was a topic hackers cared a lot about. Not so much anymore I imagine, but there was indeed a time when hackers cared if their software was open source/copyleft or BSD. Most of the online chatter was hypothetical, today it is practical.