It's a (minor, inconsequential) programming error on our part - nothing you've done, and nothing that'll affect you.
That's really not how it worked in 7.9. Any 'gateway event script' that you made in 7.9 would run exactly once...per project. If you make two gateway startup scripts, in two separate projects...you're going to end up with two scripts running on gateway startup. The same principle applies in 8.0, there's just now an explicit global project.
The gateway event scripts are gateway scoped, in that they execute on the gateway, but the actual definition is still per-project, and there is no "singleton" nature to them.