That was clearly an act of aggression. Yet Picard, instead of responding to the hostility, eagerly appeased the Romulans by decloaking within sight of the warbird and immediately confessing to wrongdoing. That was weak.
But consistent. Romulans always engage in acts of war (indeed, merely having Romulans onscreen is always and automatically an act of war because they don't have permission to come out of the Neutral Zone!). Picard never goes to war for it. Nor Kirk or Sisko, for that matter.
Which jibes well with the idea that the Feds would be giving up the right to use or develop invisibility cloaks in order to placate the Romulans. Supposedly the Romulans have the upper hand, the drop on the Feds. It's just that if they do drop, they, too, will lose - it's mutually assured destruction. But the Romulans with their invisible ships are in a better position to play MAD dogs than the Feds, so while both regularly violate treaties, the Feds technically have to be more careful about it...
Of course, the Romulans placate as well. They never go to war over anything. Here they let Picard live in "The Pegasus" even when they're within their rights to tear the peace treaty and kill 'em all.
Timo Saloniemi