I love tikz, but lightweight it is not; it’s not a huge surprise it takes a few seconds to render.
No idea what’s causing the crash, though.
I could just as easily say that Safari shouldn’t be blamed for a buggy website, but I’d be overreaching just as much as you just did.
It may have security implications, or it may not. It might just be an innocent case of someone using assertions instead of proper error reporting. Nevertheless it's a bug in the browser.
I hate this trend of hiding error messages from the user. Apple as a company known for its attention to detail in UI, should have been the one company especially dedicated to presenting a good error message without overwhelming the user with technical details—it is supposed to be the master in user communication. And it is not. Hence my disappointment.