Disclaimer: I'm a casual Linux user, not an experienced system administrator.

My understanding is that ufw uses iptables under the hood. I use ufw, yet my laptop (casual user) has iptables; don't know whether it was installed as a result of installing ufw, or if it's there by default.

Regardless of using iptables or ufw, these are both for manipulating the lower level kernel network firewall. And the article shows using iptables to load an nf kernel module. (I think) it's the module that's important, and iptables is just the convenience function to get it done.

Anyone who has root access could easily install and uninstall iptables, or use some other method of module installation.

I think.

All these tools just manage iptables or nftables rules.

Not to mention shorewall, which IMO provides a really nice abstraction over iptables, that fits 90% of the needs out there.