Vaping is all about safety first, so that is a very bad idea IMO. I can't agree with it as it misleads those new to vaping who read it and don't know the possible pitfalls of doing it.
People are not perfect, do make mistakes, get lackadaisical or distracted when they do things. So a problem with doing this can happen to anyone, even those who know the pit falls. Rob was also against this practice.
The magnet can slide and bridge the gap between the positive post and negative case, a short that could lead to a white hot battery venting if there is damage to the battery tops wrap/insulator. It's foolhardy to think it will never happen.
Some battery wraps/insulators can get damaged easily because they are lower quality than others, can get damaged/chipped in spring bar type battery chargers. So I have a large stash of IMR brand insulators and wraps in the appropriate colors (top quality), and bought a heat gun to maintain my batteries in a safe state. Of my batteries those that are easily damaged by my Nitecore D4's and the LUC's are the LG HG2's especially as they have very brittle wraps, and the Sammy 25R's. So I charge them on an Old Skol Xtar WP6 and WP2 II's instead where they can't get damaged by the charger.
YMMV