Bending a ground wire forms a coil. A coil has impedence (or inductance, if you prefer). The system, as a whole, is just that-a system. Adding an impedence into a system causes the system to operate other than "as designed". While a simple bend in a ground wire during a lightning strike is going to be somewhat irrelevant, you shouldn't do it.
The path to ground should be as low a resistance, or impedence, as possible. There are also other instances where electricity can be present on a ground wire. A professional will run a ground wire as short and straight as possible, and if it must go around a corner, it will be bent to form a "sweep". A "sweep" is nothing more than a round corner. See also "coke-can" sized bend.
