How to trigger vendors giving level-matched equipment in the Holodome and Claptrap, before Regolith Range?

Somehow I did it without entering Regolith Range, presumably by just getting to level 8?

I tried the dialogue of Zarpedeon provoking Deadlift to stop the Vault Hunters, and Claptrap's Consciousness after meeting SYS_ADMIN...

Then getting Grenade and Class Mods from Glitch Chests...

Neither changed the vendors' levels...

Is it really getting to Level 8? Or is it something else? I got the Out With A Bang LV5 Challenge, for instance.

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