If I can't add someone to a group chat on Whatsapp, does it mean they blocked me?

I created a group and tried adding someone I know to the group, but when I click on "Add participants" I can't see his name on the list. He is added as a contact on my phone but I can't see his status and when I click on his name it says "Invite them to use Whatsapp" I know that this person owns an iPhone so he already uses Whatsapp. Is it possible he blocked me (we never talked to each other on Whatsapp before, so it's unlikely) but it's just that his phone is switched off right now?

Added (1). There are many slots available in the group, and I'm able to add other people, so the problem is with this particular person.

NO it just may be that they have too many people already added