Actually I think there is an actual ambiguity in the situation and both of them were partially right and partially wrong. The teen was using a program where subsidized users get 45 min of free/low cost use of the bikes under the condition they dock the bikes after 45 min and there is a short reset period of perhaps 5-10 min during which anyone else can rent the bike.
The ambiguity is in the validity of him physically holding on to the bike during the reset period and thus physically preventing anyone else renting the bike while he waits for the program to allow him to re-book a bike.
He thought that was an acceptable thing to do. In his eyes, physical possession counts as possession, even if he is not able to rent the bike because the reset period has not yet run out.
Her position is the opposite: that the bike is unrented at this time and therefore she has every right to rent the bike. Under her position, him physically holding on to the bike is an invalid choice that attempts to possess the bike (physically) even when he does not possess the bike (legally).
I think in fact she's correct that she had every right to take the bike. As the "self-own" video shows, the fact that she was able to put the bike on her account (as shown by the bike light being lit at the start of the video and the time on her receipt), the teen did not have rental of the bike at the time. The bike was available to rent, to anyone EXCEPT the teen who had finished his rental period. If the bike rental company were ok with the prior user using the bike indefinitely, the 45 minute time limit and the short reset period would not exist. The very existence of the reset period is evidence she was correct.
However I think she was wrong to attempt to take physical possession of the bike when he was holding on to it because the risk of unwanted physical contact was too high. Even if he was doing something wrong, that does not give her the right to touch him or put hands on him to take the bike. Her recourse would be to complain to the company, not to attempt to physically take the bike. He was correct that she should not have attempted to physically take possession of the bike, but I think he was wrong to think he had the right to physically prevent others from renting it during the reset period as it was not legally his bike during that time period.