When casting Goodberry spell with a Component Pouch it is assumed that the pouch has a sprig of mistletoe to be used in the spellcasting as the material component.
Can a druid simply take this sprig of mistletoe and use it as a Druidic Focus?
The issue is about the decision making for starter equipment, if the pouch already includes a Druidic Focus you can take that out and use. Why even start with a different focus.
What good would it do?
One thing I came up with is a sprig of mistletoe is easier to hide in a pinch and even easier to camouflage as harmless in case of a pat down.
I know the Druid could simply start with a Focus anyways, but saying if they started with a pouch and then changed their mind. Maybe even use the pouch mainly after removing the mistletoe. Potentially making 'smart' enemies trying to get the pouch away from you just to grab the mistletoe and go on like nothing changed.
If you need an 'in-game' situation:
Druid loses his focus. Party Wizard gives his Component Pouch to the Druid and the Druid grabs the sprig of mistletoe since he can cast Goodberry with a Component Pouch. Most sensible way to continue is to note the pouch is missing a sprig of mistletoe and move on, Wizard can't cast any spells that require sprig of mistletoe as a material component, Druid gets a free focus.
Best Answer
A sprig of mistletoe is a sprig of mistletoe
The druid requires a sprig of mistletoe to cast his spells, which is defined in the equipment section as costing 1 gp. It's not defined anywhere as a specially blessed sprig of mistletoe or anything. You can, rules-as-written, use any sprig of mistletoe as your spellcasting focus (unless the DM rules that it must be specially harvested mistletoe or the like).
Being a sprig of mistletoe, it also meets the prerequisite for the material component for goodberry. Note that spell components are not consumed unless the spell says so.
However, there's no reason a wizard's spell component pouch would automatically contain every possible spell component for spells the wizard doesn't have, such as a sprig of mistletoe for the druid.
Rules-as-written, in chapter 10 it states that a spell component pouch can be used in place of the actual material components when casting a spell. This means the druid can technically borrow the wizard's pouch and use it in place of his mistletoe. But there's nothing in the rules which says you can take components out separately. You cast with a focus, a material component, or a component pouch, but no rule says you can divide a pouch up among the party and still have it act as a pouch.
On the other hand, as per chapter 5, a component pouch is nothing more than an empty belt pouch "to hold all the material components and other special items you need to cast your spells". The wizard's spell component pouch is nothing more than a belt pouch he uses to keep his spell components for his spells, not every possible spell component. From the realism standpoint, then, you can't take his mistletoe unless one of his spells requires mistletoe.
In short, all mistletoe is mistletoe, but you can't take one from your wizard's spell component pouch because if you're being realistic, he doesn't have any mistletoe, and if you are being rules-strict, you can't separate mistletoe from the pouch.