Out of curiosity, I went to the page of the tool and input the comment contents, which correctly caught the mistake, although tools typically miss various compound names in my experience, due to their dictionaries being limited: https://languagetool.org/
For example, I proofread my own blog posts by using the built in LibreOffice spellcheck (offline dictionary) and that has actually been useful in catching a typo or two in most of my writing. Personally, I probably wouldn't use a browser plugin due to concerns over data privacy and not caring much beyond the browser's built in spellcheck, but I personally support the overall spellchecking suggestion, as long as the tone is positive!
For some folks, the style and punctation suggestions in some of the tools out there might also be useful.
Touche.
I get the impression that the author isn't a native speaker. And as you yourself demonstrate, these things are hard for the best of us.
Ultimately though they're presumably proficient at the intricacies of malloc rather than writing, and have taken the time to share what they've learnt. Better writing will hopefully come with practice