Misfueling typically isn't a matter of putting the wrong fuel directly into the airplane (ie, hooking up the avgas truck to the jet aircraft), but of mixing in the tank.
Avgas doesn't do the damage to a turbine engine that jet fuel does to a piston engine. In fact, turbine engines, with a fuel controller adjustment, can run any number of fuels. I've run turbojets that were designed to run on avgas, and did. J34's on the P2V neptune and the C-119, for example.
If fuel contamination occurred from pressure refueling, it would have to be a tank mix. Given that Jet B and other cut fuels use gasoline/kerosine combinations and are common around the world, the introduction of avgas into jet fuel isn't going to cause engine failures. Mixing kerosine with avgas will cause detonation damage in piston engines, however.
It's not uncommon during fuel deliveries to have small quantities of mix result from using the same hoses from a truck that's carrying multiple fuels or split loads, even after hoses are flushed. More rare, over the years there have been a few incidents of the wrong fuel pumped aboard an airport fuel truck or fuel storage, from the delivery vehicle. In a large operation where the delivery vehicle is working off a fuel farm, it would take a lot of contamination to make a noticeable difference, and then in a turbine aircraft, would likely not be noticed.
Fuel will be tested as part of the investigation, confirming or ruling out this issue.