That doesn't really prove that much. They only made 3 accounts on X, then with each account they followed the 4 major parties and their leaders. Not a very good sample size.

Additionally, the underlying algo could lean toward to what causes more engagement rather than equally tailoring each party. Without having any information personally about German politics or their cultural engagement with social media, I can only anecdotally say that in America, it appears to me that the ones most engaged with social media on X are more often than not right leaning. More of the left-leaning engagement seems increasingly moving towards other outlets, such as Bluesky.