Neolithic caravan traders will sometimes sell personal shields and ranged weapons from higher tech levels.
Steps to reproduce: send in half a dozen neolithic trade caravans. Trade with them. Observe above behavior.
They sell personal shields because StockGenerator_Armor.IsValidThing always approves personal shields, regardlies of maxTechLevelGenerate. They sell ranged weapons because StockGenerator_WeaponsRanged.HandleThingDef checks the techLevel against maxTechLevelBuy, entirely ignoring maxTechLevelGenerate.
From what I read from the lore of the game, this may be intended behaviour.
According to one of the fiction primers, low-level-tech groups have been known to have, and use, high-level-tech items.
The neolithic traderkind defs have "maxTechLevelGenerate" tag, set to Neolithic, which certainly suggests that they are not supposed to generate inventory with advanced tech goods. And it partly works that way, just not entirely.
Weird.
Well, I'll leave this up to Tynan then, I suppose.
I'll mention this to Tynan but I can see how it could possibly be intended behaviour.
There are several groups of people on the planet. It is possible that the tribals somehow managed to trade for the high-tech weapons and armour with one of the more developed groups of people and just decided to bring that stuff along to trade with you.