You can argue 'foreshadowing' for basically anything in this, it's big enough and long enough that drawing dots is easy.
Of any of the reasons I'd take for Dany torching King's Landing, it's because Missandei, the last adviser she trusted, advised her to with her final word; and the time we saw she spent there hardly gave her a good impression of the place.
Irrespective of all that, I'm still of the view this series has been rushed to its conclusions and has suffered for it.