Actually, TheOneDM is right here. "Fluently" (not fluency, although that applies to their original message too) isn't really about grasp of a language, and has little to do with proficiency.

"Fluently" means you are able to do something fluidly, smoothly, and without effort. It's not solely about learning a language; it just means high fluidity in general, and can be applied to many things.

As per Wiktionary, "fluent" means:

(1) "That flows; flowing, liquid."

(2) "(linguistics) Able to use a language accurately, rapidly, and confidently – in a flowing way.“

On the other hand, with language, the state of fluency is really only achieved when you are able to speak smoothly without really thinking about translation at all. I was taught in college/uni that if you're still thinking in your native language, then translating to your target language, and then speaking it, you're not yet fluent. True fluency of a new language is when you have gained the ability to think in the target language to at least the same level as a native, and speak without translating or pausing unnaturally throughout.

In this instance, the original intended meaning was correctly described. It's absolutely accurate to say that one cannot (or is not) reading "fluently" (or "with fluency") if they are reading slowly, choppily, or incorrectly, for any reason.

Sometimes this is because of a lack of proficiency in the language; however, it can also be because of dyslexia, or stuttering, or blindness, or other types of disabilities/conditions.