Your user agent string or the actual browser code? The former is notoriously just set to whatever makes websites happy. An easy way to test is see if a current feature actually works as expected e.g. https://jsfiddle.net/fxc9a8uc/1 "test1" should be green at the top right.
It's also possible that they updated the code but didn't push the changes to the repo, which I guess is better than running 15 month old code, but also is kinda suspicious because they're not honoring their commitment to open source.