You're sorta correct, but actually I think Hewitt set the bar a lot lower than simply "classified" material.
I think what I heard him say was that if Hilary or persons acting in her stead had tried to wipe any government-related email -- even unclassified -- from the server, and if even one such official email should be found either (a) still on the original server or (b) on Platte River's backup devices, then there would be evidence of obstruction of justice.
The reasoning here seems to be that as a consequence of various judicial orders, plus the House Benghazi investigation, Hilary was supposed to turn over ALL emails that dealt with her official duties, not just the classified traffic. Any deliberate attempt to avoid handing over official email would therefore be interference with a lawful judicial proceeding and/or a congressional investigation -- hence, obstruction of justice.
O, what a tangled web we weave, When again we practice to deceive!
PS: Hilary's attempted wiping of the server would also seem to be a violation of the government records act. But that crime would probably strike the voting public as less serious than obstruction of justice.
PPS: An apology to Sir Walter Scott for the slight modification of his wording in the poetry cited above.
Yes! Sounds right.
Hillary is in very very big trouble and it looks like se is going to hang for this.