I think the answer badly misconstrues the purpose of "short term planning" and "continuous integration" as though these concepts preclude long proof-of-concept projects. The point of short delivery cycles is not to deliver a viable product to an external customer every two weeks. Rather it simply ensures that code remains in-sync with its intended use-case and guards against individuals going off on untracked tangent…
'short term planning' appears to be your construct, not found in TFA.
Short term implies reactive / tactical -- not the planned / strategic level that TFA is talking about.
It may well be that Agile 'precludes long proof-of-concept projects', given its essence is 'better ways of developing software', which clearly hides a wealth of complexity behind the heading of user-facing software.