@Joeker, As already mentioned, the Karma's ICE does turn on for a number of legitimate reasons, such as when the fuel filler door (not the gas cap) is opened, and to re pressurize the fuel system or to just exercise the ICE if you have not run it for a while. There is also a bug in the software that creates a weird stutter effect sometimes, discussed in
this thread.
When the ICE does come on, it has to run long enough for the emissions system to come up to temperature before shutting off again.
So if this is a one-time event, it's probably nothing to worry about. If it is happening a lot, however, you may need to make sure that the fuel filler door sensor is working correctly and that your fuel system is not losing pressure. In my car, for example, if I go more than 2 days on EV-only mode, the ICE turns on for a few minutes on my next drive. Since I use the ICE pretty much every day, it's not really an issue for me, but I will probably have the fuel system checked for pressure leaks at the next service interval.