Invite option in contact list

Hello,
Recently one of my contacts in the list suddenly has 'invite' option beside it. When I tap on his photo usually there are three options under the picture (chat, call and info), but now there is just an 'invite' option. What does it mean?
I've had chat sessions with him 2 months ago just fine. But, recently I sent him a message and only got one grey tick mark.

What has possibly happened? Did he delete his account? His account got expired? But more importantly, did he block me (I read that when I only get one grey tick mark, then I might be blocked)?

Thanks in advance for the help!