Is an item's Caster Level the Minimum Required Caster Level?
For example a Bag of Holding has a CL of 9th
Aura moderate conjuration; CL 9th
Does that mean a creator has to have a Caster Level of 9?
No, the relevant rules can be found in the entry for Magic Item Creation in the Pathfinder SRD.
To briefly summarize, the caster level of the item is part of the DC that you need to roll against when you make a spellcraft roll. (nominally 5 + Caster level of the item).
It also set other characteristics of the magic item such as how difficult it is to dispel.
Creation of a magic item is controlled by several prerequisites all of which are listed in the construction requirement in the magic item description.
For example Ring of Protection requires you to have the Forge Ring Feat, know the Shield of Faith spell, and have a minimum caster level of three times the ring's bonus, and pay the costs from the attached table. Shield of Faith can only be cast by a cleric, oracles and/or inquisitors. Finally will need a spellcraft (or craft) roll of 10+ due to it's caster level of 5.
This also has been addressed on an official FAQ:
Pearl of Power: What is the caster level required to create this item?
Though the listed Caster Level for a pearl of power is 17th, that caster level is not part of the Requirements listing for that item. Therefore, the only caster level requirement for a pearl of power is the character has to be able to cast spells of the desired level.