I also read it as "software critics" but isn't it grammatically correct? Maybe our minds mess it up given the context and our backgrounds.

It's written in headlinese [1].

[1] https://en.wikipedia.org/wiki/Headline#Headlinese

A comma would also work, but I don't know if you can use commas in HN titles.

...seeks ban of software, critics say

That doesn't seem right to me.

Indeed. Wouldn't be surprised if San Francisco tried to ban software, and criticism too. Perhaps "Software, critics, and software critics seek to ban San Francisco."

This would be an improper use of a comma.