The short answer is at the molecular level, they are similar if not the same. From a functional standpoint, no.
To elaborate, epoxies typically come in a a 2 part system which needs to be mixed together.
Part A is the actual epoxy, which is basically a molecule with 2-4 epoxide groups, which look something like:
C - C - (Rest of molecule)
\ /
O
Part B is the curing agent. Typically it is amine (nitrogen) based, though it can also be mercaptan (sulfur) based. There are multiple reactive sites on the curing agent molecules.
During the chemical reaction, one of the oxygen-carbon bonds opens up and reacts with the curing agent. Since there are multiple epoxide groups on each molecule and multiple reaction sites on each curing agent molecule, you end up with a sort of uber-molecule (we engineers call it "highly crosslinked").
So pretty much all epoxies have the same basic mechanism. But there are dozens of alterations that can be made. Each time you change your Part A or Part B, you get a product with different properties (i.e changing your curing agent from one with 7 active sites to one with 13 active sites). Furthermore, you can add stuff to the epoxy to thin it down or thicken it up.
When somebody mentions epoxy in the context of modeling, I tend to think of the 5-minute or 90-minute systems you buy from the store. Typically they come in a thing that's essentially 2 syringes molded together; you dispense, mix, and apply. It has a consistency similar to honey.
The putties are much thicker (like play-doh or silly putty), and are probably good for carving/molding (like zimmerit). It's been several years since I've tried using it, but would guess that it's a marginal adhesive at best because it doesn't wet out the surface that well.
Hope this helps.