Those are probably some good guesses. My friends were trapped at the Akron airport for 5 hours with little to no information being offered other than "storms" - even though as you note the storms hadn't actually reached NYC for most of the time they were waiting.

And yes, Frontier only has a couple of gates at LGA, B1 and B3 I think, so that may have been a factor. I have indeed sat on the runway after landing while waiting for the gate to clear.