Was having the same problem. Fixed it by disabling the adding events from Gmail automatically according to the Google instructions. I would rather choose what hits my calendar anyway.
I wish you could whitelist instead of just having a black or white option. My SO and parents I can trust to inject events (keeping track of stuff they've planned but I forgot is 90% of my use of Google Calendar honestly) but now that spammers have discovered Calendar as another place to spam/phish it's less hands off.
I'm getting the same spam/events. What's really weird is I'm pretty sure all of these emails are getting sent to spam but gmail/gcal is still adding the events to the calendar.