Wow.... That is blatantly wrong. (Not at Hectic, but the excerpt from the email).
Here's whats up.
Lower Receiver on an AR pattern rifle is a PROHIBITED ITEM (for other guns it can be upper, ie. MP5, basically where the serial number is located on the real steel counterpart). This means that you are PROHIBITED from importing it unless you get a waiver of some sort, or exception (eg. Mil/LE), or have a BFL for props (eg. why the production crew of Stargate can get prohib stuff to use in their TV shows).
Now, with that said, the way ASM worded their email is totally wrong. With the above said, it's technically legal and in a bit of a grey area as far as import goes (under certain circumstances). It could be seized but could also pass through so it's a bit of a crapshoot. For more information I'd suggest getting AV'ed and perusing the info threads in the AV only section as I don't want to have to reinvent the wheel and/or possibly give wrong information.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE