It's Caster Level 8
Your second interpretation is correct. Here's the rule itself:
Creating a magic weapon has a special prerequisite: The creator’s
caster level must be at least three times the enhancement bonus of the
weapon. If an item has both an enhancement bonus and a special ability
the higher of the two caster level requirements must be met.
Then from the Magic Weapons page:
In addition to an enhancement bonus, weapons may have special
abilities. Special abilities count as additional bonuses for
determining the market value of the item, but do not modify attack or
damage bonuses (except where specifically noted). A single weapon
cannot have a modified bonus (enhancement bonus plus special ability
bonus equivalents) higher than +10. A weapon with a special ability
must have at least a +1 enhancement bonus.
From here, it's pretty clear that enhancement bonus and special abilities are distinct things. You combine them for the weapon cost (as the rule stats), but not for the crafting caster level requirement as each type has its own requirement. You just have to be able to meet all the requirements.
Thus, you need CL 6 (3x2) to make a +2 enhancement bonus, and CL 8 (and have access to the spells Chill Metal or Ice Storm) for Frost.
This also means all the weapons on the chart can be created without being epic level, as if you needed to be CL 9 to make your +2 Frost Weapon, it'd be impossible to do any combination that is >= +7 without epic levels. (You can't make a +7 sword without epic levels, but you can make a +5 Keen Frost one, which has the cost of a +7 equivalent weapon.)
It Could Be Caster Level 6
Depending on how you want to interpret the rules around prerequisites, you could create the weapon at CL 6 as a Druid (who get access to Chill Metal at level 3). The reason for that is these rule passages. From the SRD:
While item creation costs are handled in detail below, note that
normally the two primary factors are the caster level of the creator
and the level of the spell or spells put into the item. A creator can
create an item at a lower caster level than her own, but never lower
than the minimum level needed to cast the needed spell.
And from DMG p. 215:
For other items [besides potions, scrolls, and wands] the caster level
is determined by the creator. The minimum caster level is that which
is needed to meet the prerequisites given.
Depending on how you read this, the prerequisite could only be access to the spell itself, rather than the CL listed. In that case a level 6 Druid could create the item (as they can do both +2 and have access to a required spell). A Sorceror would need to be level 8, as that's when they get access to Ice Storm.
I'm not 100% convinced this is how they intended it to work, but it makes an item entry like Universal Solvent make a lot more sense. It has a listed CL of 20, which for such a common an inexpensive item just seems really wonky if only the greatest spellcasters on the planet are able to create it (particularly since the required spell is available to Wizards at level 9).
If you use this interpretation, the CL listed on the item entries is a guideline, or what you'd expect a normal item of it's type to be if you find one in the world.
