Comment by unscaled
The difference that you've already noted here is that the X-Browser-Validation is new. It doesn't have to keep using SHA1, MD5 or CRC-32 to maintain compatibility with a protocol spec that predates the existence of newer algorithms.
The header is new, but what's it working with on the server side? Were there any other considerations for the selection of the value?
Though in contrast to that, sometimes the criteria is just that a given number of bits aren't useful, so the output of a different hash is truncated to the desired size.
Maybe part of the driving criteria os compatibility with E.G. the oldest supported Android version? Or maybe some version of Windows seen in legacy devices in poor countries? There might be good reasons beyond just 'header is new, everything must be state of the art'.