Why is that ironic? Lots of sites struggle with traffic when they hit the front page here.

Because it's about signal strength, but also the hostname is "nick vs networking". And if your site can't handle a few hundred requests per second (which I seriously doubt the HN traffic is anywhere close to) on a static web page, then you're doing something wrong

I assume the irony is that an article about signal strength, which is closely related to data speed, is loading slowly because the site servers have slow data speed.