Most likely right.
I think it has everything to do with stamping out the reselling of gifts, not exploitative cross-region gifting. Valve took a baseball bat to the latter in early 2015, when, to discourage VPN activations, it added a runtime restriction on top of the activation restriction attached to gifts purchased in regions that have notably cheaper prices by default and, unlike before, applied this to all spare gifts retroactively. Traders with older, say, RU-purchased gifts that were previously region-free woke up to find themselves with a collection of digital paperweights as they were now only of use to Russian users.