In a general sense, it is true.

When being flagged, Rep acts as a gatekeeper, and decides if rep will decline or not.  Only the strength of the flag (rshares behind it) controls how much of a decline.

When being upvoted, no check is made for rep at all, nor does it influence the amount of rep gained.  This is a commonly misunderstood fact about the blockchain.

That post you reference doesn't actually state anything useful to this conversation, only explains how rep is calculated on the blockchain, not how it is distributed or taken away.