This is just going to feed more conspiracy theory nutters.
First, a 1 in a 100 billion chance is absolutely nothing. There have been hundreds of millions of infections in humans, each representing billions upon billions of replications of the virus. Every replication carries the chance of mutation. Given that,
Second, mutations, whether random or not, are subject to selective pressure and incremental progress. A mutation that moves a sequence just slightly in the right direction, coding for a slightly different but close protein, will be selected for. Basically, evolution optimizes some structures (and therefore sequences) by hill climbing, accepting mutations that improve fitness and discarding mutations that don't. It doesn't roll all the dice at once and start over every time.