With DEC, we have (for a very, very long time, if not always) returned the extra card(s) to the location from which they were drawn (usually top of the library, but could be a face-down exile pile, even a sideboard). We do not shuffle in this instance - that card is meant to be drawn, just not yet.
The correct way to parse that sentence:
- was the card known (revealed) to all players before being placed into the hand?
- if not, was it placed into an empty hand?
- if either of those are true, can it be put back with minimal disruption?
Note that, if more than one card is drawn, the tests are applied to all the cards; if the hand was empty before drawing 3 cards, then the second test is true for all 3. (Yes, some have argued - unsuccessfully - that the 2nd & 3rd cards didn't go into an empty hand; that is an incorrect application.)
d:^D