Hi - That’s because in the video @wisebubbler is using ‘Oauth2 User-Agent Flow’ as the Authentication method, so Bubble ‘automagically’ handles the refresh token/new key part for you.
Whereas in the first set of instructions you followed Google Calendar API use case - #7 by mebeingken @mebeingken is using ‘Non or Self-handled’ so he had to build a workflow (which is detailed in that post) to handle the refresh token part.
I would start by going down the first route as it’s much easier and if you hit issues later on then go down the second route.