Yes - “not held” refers that agent is not required to trade at any specific price or specifc time interval, if compared with simple market order.
The agent has more discretion (not held) here, as he may choose to even wait till the next trading session if he believes that he will likely get better pricing.
I think a good intution may be - he is not held liable if the trade is not executed in the first go.
I understand that market order is more focused on execution certainity than pricing but this variant gives agent more discretion.