If caster level requirements to make magic items were "an error", then it stands to reason that statement applies to caster level requirements to attain the feats needed to make magic items.
Short of Monte Cook showing up in this thread and explaining what he meant by "an error", we are left only with the semantics for interpretation. And "caster level requirements to make magic items were 'an error'", to summarize, logically applies, at minimum, to any 'artificial' caster level requirement to make a magic item. From that, the chain of logic follows as stated, and the only caster level requirements are the ability to cast, or access to, the needed spells.
However, Monte Cook may not have meant something that all-encompassing, and may have only meant, as you state, "caster level requirements...on the actual magic items themselves...were 'an error'".
While I think the game would be enhanced by my chain of logic, that is far from being authoritative.
This is how it's supposed to work. I'll use 3.5 items because the 3.5 SRD is readily available online, but the principle is the same for 3.0. Take the
amulet of the planes:
CL 15th; Craft Wondrous Item,
plane shift; Price 120,000 gp.
If you find an
amulet of the planes as random treasure, or buy one, the caster level is 15th. However, that is
not a prerequisite. The only prerequisites are the ones listed as prerequisites: the Craft Wondrous Item feat, and the
plane shift spell. These in turn give you virtual prerequisites of 3rd and 9th level, because CWI has 3rd level as a prerequisite, and
plane shift is a 5th level spell. If a 10th level PC acquired the resources to make this item, they could, and it would have a caster level of 10.
Let's look at another item, the
amulet of natural armor:
CL 5th; Craft Wondrous Item,
barkskin, creator’s caster level must be at least three times the amulet’s bonus; Price 2,000 gp (+1), 8,000 gp (+2), 18,000 gp (+3), 32,000 gp (+4), or 50,000 gp (+5).
Again, being 5th level is not a prerequisite. However, this item does call out a level-based prerequisite, so in order to make an
amulet of natural armor +3 you need to be 9th level.