ENT showed us Romulan cloaking technology and more than once, even if TOS seemed to think it was a shocking new development and nobody on Kirk's Enterprise had ever seen such an invisibility screen. There are ways both can exist and not violate canon, in part labeling the Romulan minefield of 2152 as different technology than the Bird-of-Prey cloak in 2266, even if both use roughly the same principles to achieve their intended results.
Or maybe, it’s a shock that the Romulans use cloaking technology on their vessels in the 23rd century, since they never used them in the war. And disguising their ships with holoprojectors was more the Romulan style back then.
Maybe that cloaked BoP in ENT was an outlier from what actual BoPs were actually like during that era.