Google is testing not just large titles for grouped snippets but also large titles that are fully bolded for Google Ad results.
Here is a screen shot from Andrew Rodgers who shared this with me on Twitter:
Google is not bolding the title because it matches anything in the search query box. It is just bolding the title because it is testing a new look, I suspect.
I do not like bold things… 🙂
Forum discussion at Twitter.
It is not just ads I am told:
Update in 2022: More bolding font tests:
Update in 2023: More bolding: