They claim to have 406M unique visitors monthly.
If that is the case, it isn't shocking to see them at #7, only surprising that a lot of people working and living with tech since forever never heard of them
Glam properties on Compete:
Glam.com = ~700k https://siteanalytics.compete.com/glam.com/
Ning.com = ~2 million https://siteanalytics.compete.com/ning.com/
Foodie.com = ~307k https://siteanalytics.compete.com/foodie.com/
etc
So these rankings are not based on singular properties. It probably combines Glams other properties such as Brash, Bliss, Foodie, Tend, etc. They have tons.
Which may be fair since Yahoo is a series of sub-properties, although the branding is more consistent than Glam.