> If they were solely written languages then you wouldn’t be able to, for example, read the text aloud, right?

I believe /u/Tor3's point is that Norwegians would read and pronounce nynorsk and bokmål the same regardless of the differences in the writing.

> Isn’t it similar to English in this sense?

It is. I don't pronounce English words differently when they're written with e.g. British or American spellings.