More importantly, blindly increasing all of your 32-bit integers to 64-bit is going to double your memory usage, and ultimately just mask the real issue (i.e. improper bounds checking).
They made a mistake for sure, but 32-bit vs. 64-bit architectures should not be on trial.
The real impact on memory usage is likely the 8-byte pointers, but if you have a non-trivial amount of memory, it's rarely an issue worth fretting about.
If we cared about pointer sizes, we'd still be writing 16-bit code.
Running 64-bit would have "prevented" this bug simply by virtual of that fact that the default datatype would have been big enough to avoid overflow, but it isn't really a solution. I just find 32-bit vs. 64-bit to be inconsequential to the real mistake, which was an improper software development process.