If the only defense were triploidy I might be concerned. But what the developer has done is employ what's known as "defense in depth" in security arenas. The triploidy defense is monitored with flow cytometry, precisely because it isn't 100% foolproof (this is like the intrusion detection system that monitors for people who get through your firewall). The salmon are raised in enclosed pens, in a landlocked area in the Panama highlands (this is like an airgapped network, not connected to river systems that reaches the ocean in the way that nuclear networks are airgapped from the Internet).
Even if a malicious employee smuggles a fish out, and somehow keeps it alive until it can reach its natural habitat, it still won't reproduce because it is triploid. And it isn't clear to me what possible benefit there would be to this, except maybe for anti-GMO activists looking to smear the industry. Do you think they'd deliberately try to sabotage an ecosystem just to make a point about the risks of accidental release, where accidents have been effectively eliminated?