It's true that people outside the UK signed the petition. But scroll down and you will see:
"name": "United Kingdom",
"code": "GB",
"signature_count": 2764418
2.7 million is a lot of signatures in a short period, but I completely doubt there will be an election, even if more are added.
In addition, a breakdown by UK voting region is given.
What we don't know is how many are duplicate signatures and how many are legitimate.
So, according to Fullfact, you can use the same email address twice, but only twice, and any other signature will be discarded.
Is it possible to repeatedly sign a parliamentary petition using the same email address? – Full Fact
How is it discarded? If it detects the IP address, then maybe it can detect the same person using a different email address? Or maybe not? I have no idea.
As stated, I don't think there will be another election until Labour have completed their full stint, although there may be a leadership change at some point. We will have to see.