It sure is. They're kinda the same. Akkadian is the oldest form of the language, spoken by Sargon of Akkad. Fast forward a few hundred years, and there's two dialects: Babylonian in the south, and Assyrian in the north. Like Ibrahim said, they were dialects (of Akkadian) that were probably mutually intelligible.
As for the reason Seleukus had this written, the shortest answer is because Alexander did it! We indeed have a few cylinders with his name on it (see the link in the original post). As for why Alexander did it, it's because the Persians did it. Back when the Persians took power from Nabonidus, the last Babylonian king, Babylonian culture was very strong compared to the Persians. They continued a lot of the Babylonian traditions, and even claimed to restore them to their rightful glory.
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