From an airport security perspective this is a success because the individual was not able to either access an aircraft to place a prohibited item on board, nor cause any other act of unlawful interference. However, others will look at this as a failure of the system because the individual was able to access the secured area of the airfield. This question can best be answered by looking at the gaps in airport security.
There are essentially three types of gaps in airport security. First, there are certain gaps that cannot be closed for air travel to even work. As long as there is commercial air travel, there will always be some gaps of varying size within the system that exist to facilitate the entire air travel process.
Second, there are gaps within the system that are just too expensive to close. At some point there’s only so much money you can throw a little problem before you hit the point of diminishing returns.
Third, and most concerning, is that some gaps have yet to be identified or exploited. Just as every sports team tries to come up with a new strategy to defeat their opponent, terrorists continue to develop new strategies and tactics to try to defeat the aviation security system.
The goal of aviation security practitioners is to identify the gaps, closing those that can be closed, and reducing the size of those that cannot be closed to the smallest extent possible, that still allows the system to operate in a sustainable and fiscally sensible manner.
Just as it is with an individual jumping the perimeter fence, an individual accessing the airfield through the baggage belts is an obvious violation of the security system, but other layers in the system prevented an act of unlawful interference from being carried out. Baggage belt are a necessity and to place additional security personnel, alarms and CCTV systems to monitor the belts, for the very rare event of an individual trying to crawl through to get to the airfield or a plane, is not a good use of airport money and resources. There are other layers in the system to prevent an individual who accesses of the security area through a bag belt from getting to an aircraft or affecting a different sort of attack, and in this case, the other layers worked (also, crawling around on baggage belts is a good way to get hurt so there’s a inherent level of security here as well).
All personnel who work at a commercial service airport in the U.S., are required to challenge any individual that is in the security areas of the airfield and not in possession of a valid airport identification badge (known in the industry as a SIDA* badge). If someone cannot present a badge, the individual conducting the challenge is supposed to ask the person to remain there while he or she contacts the airport police or security personnel. If the person leaves or runs then the airport person is only required to attempt to maintain visual contact and provide descriptive details to the police or security personnel when they arrive. In Miami, airline workers apparently tackled the individual, which goes beyond the typical required response.