Could be it means .40 or bigger, or it could just be a clever way to separate the non-calibers (.22, .32, .380) from the legitimate big 3 (.40, .45, and 9mm all start with a 4 or bigger).
I guess you could squeeze the .357 Sig in under the label “9mm Magnum”. Ditto for 10mm.
.357 Magnum seems to be the only problem, but then again if you have any choice in the matter you don’t want to be defending yourself with a revolver.
9mm IS .357 inches; ergo less than “4”.
10mm is .395 inches and is a more powerful cartridge. It may qualify as an honorary .40. But then, how many obscure calibers do we need?
In my opinion, the only reason for carrying a .357 sig (other than an affinity for obscure calibers) is that you are Asian and regard “4” as an unlucky number.
On that note, I have a friend (Asian) who owns two Sig’s - a 9mm and a .357 sig. You may find it difficult to believe but the brilliant guys at Sig Sauer designed the P226 so that clips from the 9mm will fit in a P226 chambered for .357 sig. My friend accidentally slapped a 9mm clip into his .357 sig at the range and fired off a round. It discharged but the badly expanded case stovepiped. Didn’t seem to hurt the gun though. The moral I guess is, if you must own two Sig 226s, always leave one locked up at home along with its ammunition.
And if you’re Asian and don’t want a 40 something caliber weapon, plunk down the big bucks and get a Desert Eagle.