Even if you had managed to come up with a point by selectively quoting the post, that would still be bad. The good-faith way to engage with somebody’s post is to reply to the meaning of the overall post. It might be necessary to cut some parts out for logical flow, but that shouldn’t change the meaning of what you are replying to.

Attacking a point by attacking its supporting points is a pretty standard way of going about arguing.

Sure, but not just by contradicting arbitrary sub-sentence snippets of text devoid of context. An attack against a supporting point should be related to the way that it supports the overall argument.

It’s fully the first half of the comment rather than a few words taken out of context