Cactus Web Site special offer: Orders over $75 will receive a free Angel of God 2023 National Promo card while supplies last.
Unless they say otherwise, all cards default to play with their targets. Cards in hand are not in play, so Lampstand does not protect them.
Lampstand does actually say otherwise. "Not in battle" is it's own location, which includes territories, set-aside, and the Land of Redemption. It does not cover hands (so the answer to the original question is no it does not), but it does cover the Land of Redemption, so your explanation isn't quite right.
I don't think they're going to errata the card, what has changed is the definition of "not in battle" (which is a game rule/definition, Lampstand just happens to be the only card that uses the terminology currently). Currently, "not in battle" is defined as Chris mentioned.
It's actually found on page 122 of the REG (I, myself, was surprised to find it was in there).
I want to know if you can play mayhem or vain philiosophy with lampstand still active?