This blog post[1] from the developer helped me to understand this better. It's linked on the github page, but I wanted to provide the link for more direct clarity.

Astonishingly, we can process 20 years’ worth of data, sampled every five minutes, in less than 20 seconds.

That sounds quite promising.

[1] https://tech.target.com/2018/12/11/matrix-profile.html