To be fair, they claim the adblock engine saw a 75% reduction in memory usage, and in the images they're showing the main browser process generally (I assume? I don't use Brave), or which the adblock engine is only a part but had a substantial impact on usage.

That is correct.

thanks for the clarification. is this 45MB reduction for the whole browser? or is this 45MB per tab?

"Brave has overhauled its Rust-based adblock engine to reduce memory consumption by 75%"

This only claims that the memory usage of the adblock engine was reduced, not the total memory consumption of the browser.

I'm guessing the same kind of people who don't understand the difference between 0.002 dollars and 0.002 cents (http://verizonmath.blogspot.com/2006/12/verizon-doesnt-know-...).