That doesn't look like engine oil. However, it does look like it did a great job cleaning the engine.
I'd put some fresh engine oil 5W30 if working in cold temps or straight 30 or 15W40 if working above freezing temperatures and put it to work. Before doing that though, I'd take a compression reading just to see if there's a chance the oil didn't provide sufficient protection. If compression is good, I'd be willing to wager the rest of the engine will be fine.
Nonetheless, I'd most definitely advise the vendor of their error, bring them a sample of the oil and have them agree to an oil analysis. If in fact it is hydraulic fluid, I'd look into the possibilities of potential negative effects it may have had on the engine.
If there's a serious concern that damage may have occurred, I'd return the splitter and have them replace it with a new one, or, at the very least, cost out a new engine, and have them replace it.
Here's some interesting reading:
"Both hydraulic and engine oils are made from base oils with additives mixed in. The additives used change the characteristics of the oils so that they function differently.
Generally, hydraulic oils (final product including additives) are expected to have very low compressibility and very predictable friction and viscosity stability under pressure.
Engine oils (Engine Lubrication Oils anyway) are intended to have high resistance to heat (degradation including chemical and viscosity due to heat) resistance to burning and resistance to absorption of fuels and chemical compounds produced during combustion.
Both classes of oils are likely to have additives intended to provide detergents and to reduce foaming.
Base oils are most commonly petroleum oil bases due to cost, but other bases oil can be used including mineral oils (especially for hydraulic oils) and plant oils (especially for engine oils) and oils from animal sources."
Considering that you smelled gasoline in the oil, it would further lead me to believe that it's hydraulic fluid.
If there's hydraulic fluid in the engine you have to wonder if there's engine oil mixed with the hydraulic fluid in the reservoir?