He might be interpreting the claim as being that Snowden could do that, which is, of course, false.
Alexander might have meant Snowden wasn't supposed to have that capability. Or that Snowden had it but wasn't supposed to use it that way, so he "couldn't" do it under the law (but could in practice).
It's hard to say; the testimony has often used obfuscatory weasel words and conveniently shifting definitions, and the avuncular grandparents in the Senate aren't exactly vigorous in their cross-examination.