In an exchange from March 2012, Johnson had an opportunity to question NSA Director Keith Alexander about precisely the kind of concerns that the exposé of PRISM confirms — that the signals intel agency can spy on content coming through American Internet servers.

I think it's pretty accurate description of what PRISM and other NSA programs allow NSA to do. Also:

Alexander categorically denied more than once in this clip that NSA even had the capability to conduct surveillance in the manner Wired reported

We now know not only they have the capability, they are actively using it. If claiming such capability does not exist is not a lie, then what it is?

The part you quoted is correct, but he didn't claim otherwise. He said that they could not get Americans' data in that manner, which is true. Reread his exchange with Johnson in the article. ("Does the NSA intercept Americans’ cell phone conversations?") In other words, he did not lie.