Look, it is 54 KB. That is not large. Perhaps with some effort it could have been slightly smaller but the author is probably optimising for a different metric.
You're right. 53,966 bytes and not one larger. I wonder why it chokes up my browser.
But seriously, if you're going to use a GIF, at least make it animated.
Granted, the CSS wouldn't require zooming in, and the citation link would be usable.
The image dimensions are 1120x13800, so it's 59MB uncompressed in memory.