Hi Daniel,
Glad you found the script useful.
It's as you said, Google has set limitations on the number of times you can call the URL Fetch method in particular. The current quota is 20,00 requests/day for free google accounts, and 100,000 requests/day for workspace accounts. You can read about it here https://developers.google.com/apps-script/guides/services/quotas
So let's say you have 500 rows in a sheet running the script and fetching the data. Whenever, you open the sheets page or refresh it or someone else opens it those generate 500 requests each time. So it should take 40 page visits/refreshes to reach that quota. Unless there are other Google events that trigger them as well.
I admit I wasn't aware of this limit at the time of writing the script. I added a new section to the article with the updated code to address this issue. You'll likely have to wait another day for your requests quota to reset.
Thanks for bringing this to my attention!