Good attempt to try and guess the meaning but you are a little wrong. Firstly, seize is always used aggressively, meaning to take or grab with force. So even the translation you had done has a slightly different nuance because "held" is too soft of a meaning. Secondly, if it were referring to the man's arm, the preposition would be "with" not "by". Also in reference to who is doing the seizing, if it had have been the man, it would have used his hand not arm.

Two things: 1. "Seize" implies something aggressive, sudden, and probably unwanted. Police "seize" your items when you're under arrest. Robbers "seize" your money when they're stealing from you. 2. "by the arm" is about the woman's arm, not the man's. (I think you were confused on whose arm). You can grab (or seize or hold or carry or some other verb) someone by the arm, or by the ear, or by the ankle, or by - well many body parts. But when we say "Pat dragged Chris by the nose" we mean that Pat is somehow holding Chris's nose.

I agree with Samuel. The translation is correct, but Samuel's explanation that it is with more aggression is correct. It makes me think of a negative and somewhat scary situation. Or it could also be positive in the sense if someone seized someone else's arm to help them away from a scary or dangerous situation. For example, "She seized her daughter's arm in order to keep her from running into the busy street."

Yes. Another way to say this is " he grabbed her by the arm." But what you were thinking of is something like"he put his arm around her."

"Seize" is a quicker, more aggressive version of "take", "hold" or "grab". The sentence "he seized her by the arm" gives off an impression of him using force to stop her, by grabbing onto her arm.