It can be dangerous to backfeed (which is why you're supposed to have an interlock for a generator inlet, ensuring utility power is disconnected). But:

1. These grid tie inverters are designed and tested to shut off completely if there's no grid power. (This is a big design tradeoff: it means they don't provide any power during a grid power outage, even if it's very sunny out.)

2. Even if I had a beefy generator that was unsafely backfeeding my house while the utility power was still connected, the generator would be trying to power not just my house, but all my neighbors too! And the circuit breaker and/or inverter on the generator would likely trip and shut down almost instantly.

There's still a possible risk from #2, especially if the downed wire being repaired is relatively local (i.e. your house only).

But I think #1 and #2 mitigate this risk very well.