Probably was submitted with the correct title and then rewritten by the HN title modification ruleset.

I think submitters are able to correct the title for a while and that when they do it might(?) override some or all of the rules in the filter. But the time window for doing so has probably been passed now.

Mods could still change the title though.

Either to the original:

Implementing Rust's dbg! in Python

Or if they want to help out those unfamiliar with Rust syntax they might make the title be:

Implementing Rust's dbg! macro in Python

And if they are opposed to use the bang even in this context it would then be fine IMO to either preferably set the title to:

Implementing Rust's dbg macro in Python

Or less preferably to set the title to:

Implementing Rust's debug macro in Python