Here it says that Readlang calculates a readability index as well as the percentage of common words (based on movie subtitles): How does Readlang know the difficulty of a text?
I could imagine that the readability of your text is rated more difficult since it contains some longer sentences. Newspaper vocabulary also differs from movie subtitles.
I had the different experience that I uploaded a Spanish text which was rated as A2 but I would say it was more of a B1/B2. The reason could have been the format, because it was a theatre play with a lot of poetry and line breaks, which might have lead to a high count of seemingly very short sentences.
On the other hand I had the story bot generate some intermediate stories for another language and they came up as A2, B1 and B2. They were quite similar in terms of difficulty of grammar and sentence length, but the B2 text definitely contained more obscure vocabulary due to its topic, so I’d say that these ratings made a lot of sense.