You're right in that it is very broad. As an example, if an overdose were to occur at a rave party, there may be dozens of people there. Would the precision here apply to everyone at the rave? Perhaps there's a way of narrowing it.
Again though, it does depend on the bill's sponsor's intention. Listening to his explanation, my sense was that he thought that it should apply to a fairly broad category of individuals. Perhaps that is his intention.
My concern would be that it would cover off a number of people who would have had nothing to do with seeking assistance. This bill targets the person who calls for or seeks assistance for someone who is overdosing or the person who is overdosing and seeking assistance for himself.
To provide an exemption from the possession offence for virtually everyone else who is in an undefined space might make it a little difficult for police to actually interpret what that means. If you were to characterize it or limit it to “in the immediate vicinity”, that would help to some extent. You would then end up with a somewhat similar problem in that you would have to define what “immediate vicinity” would mean. At least it would be some measure of constraining the application of this provision.