Simply disobeying god is sin enough. Man and Women did know what God meant and even restated the command to the serpent. Thus by having this knowledge, though tempted by satan, they still sinned.
Also, bearing false witness was not givin until the 10 commandments were givin. The 10 commandments are not expos facto. Also, it is neither of a false witness nor false testimony as false testimony is defined as "FALSE TESTIMONY - Testimony is "false" if it was untrue when it was given and was then known to be untrue by the witness or person giving it. A statement contained within a document is false if it was untrue when used and was then known to be untrue by the person using it." by lectlaw.com.
Edited by herrmann, : No reason given.