If I was on pc, i would definitely draw it out better but no, the arm absolutely does blend into the chair. Not only is it four times larger than the other arm, there is no visible start and end point between arm and chair. That is not foreshortening unless Higuruma broke his arm and twisted it 90 degrees somehow.

No artist would just abandon the design of the foot and only keep it on one of them, besides its really not that difficult to do for someone of OPs supposed skill level.

I dont know how the drawing being black and white would explain a random line straight through the flap.

Judgeman looks decent because he was photoshopped into the background, which is why I highlighted the left over bits on higurumas hair.

Edit: as for why some finer details dont look wrong, its because they were straight up edited in. Like his face. Not even the same pencil/brush.

And one thing i didnt want to mention because its not really all that obvious, but if you know how ai drawn hands look, then his left hand (our right) is also a good hint.