False positive: `defusedxml` is reported as a build tool

[SnoopJ]

A Python package that depends on the safe XML parser defusedxml causes brief to produce a report that this library is related to the build.

Reproduction

17:07 [jgerity@giskard /tmp/brief_repro]
$ ls
pyproject.toml
17:07 [jgerity@giskard /tmp/brief_repro]
$ cat pyproject.toml 
[build-system]
requires = ["setuptools"]
build-backend = "setuptools.build_meta"

[project]
name = "dummy"
description = "Dummy package"
dependencies = [
    "defusedxml>=0.7.1, <1",
]
17:07 [jgerity@giskard /tmp/brief_repro]
$ brief 
brief 0.5.2 — /tmp/brief_repro

Language:        Python
                 1 runtime

Build:       defusedxml

4.4ms  472 files checked  2/516 tools matched

(as an aside: why 472 files? does that include the contents of setuptools?)