As you may guess I'm no bible scholar but my guess would be that the bible, being a collection of writings that was put together, is likely to have parts that were difficult to put together and where there may have been dispute as to which book a particular text was from: and so at least in this case it was attributed to both? That sounds plausible to me.
bad editing, perhaps. The books of the bible weren't originally in a bible, they were separate preachings; editors gathered them together. Two different prophets may have recounted the same thing, and the same account was used twice; or maybe only one prophet said it but it was inadvertently used twice.
Isaiah is split into 3 parts. cpts 1-39, 40-55, 55-66. Although I believe the syntax and word usage changes at cpt 37. Isaiah wrote 1-39 circa 8th century BCE so Isaiah wrote cpts in 2Kings too. Syntax and prose 100% the same.