To be rather obtusely specific, the FBI has not requested a change in product or even the design of a new product from Apple. I'm sure the FBI was well aware of the subsection of the US code the article is referring to which is why the request was framed as a "one-off tool" to help in an investigation, not a new product, and it's why the FBI itself is not saying it can require Apple, but rather that a court of law is saying Apple has to.
Again, this is nitpicking and IANAL, but the limitations section [1] is pretty clear that law enforcement itself cannot impose any requirement as to...
[...]require any specific design of equipment, facilities, services, features, or system configurations to be adopted by any provider of a wire or electronic communication service, any manufacturer of telecommunications equipment, or any provider of telecommunications support services; or[...]
The request being made isn't really covered by the limitations here. While I have full confidence that the end-game of this case for the US government is to add an exception for the creation of "one-off" tools, I don't think that the FBI's request is actually covered by this limitation.
The authority of the request doesn't come from law enforcement, it comes from a court, fulfilling the intended limitation that law enforcement can't dictate the design of communication technology for its own purposes.
Likewise, while a product of sorts is being created in the form of a law enforcement tool, the FBI isn't actually asking for this to be implemented in the product itself or requiring that Apple make it the standard either.
Furthermore, the entire section is discussing the ability to monitor, capture, and terminate communications, not talking about software or hardware itself, which his shared by the statement released by the FBI. [2]
Again, cannot stress that I am not a lawyer, but I think the interpretation on CALEA is fairly sound - it's not applicable as the purpose of the section being referenced is not relevant to the request being made. I do think that the request is still wrong regardless of any reasons put forth by the FBI and that it sets a horrible precedent, but this article (and by extension Apple's lawyers) are arguing a weak point using CALEA.
[1] - https://www.law.cornell.edu/uscode/text/47/1002
[2] - https://assets.documentcloud.org/documents/2755290/2016-03-1...
edited for clarity purposes