Grey or blue quotes

Hello everyone!
I'm facing a weird situation (well it seems to me). I'm receiving messages from one of my contact but last time he's been seen was 2 hours ago or more... How to explain this?

More ove I can send a message, then I can see the two grey quotes that qtays greys but I'm receiving a message from my contact and my previous post still have grey quote.... Ho to explain this also??

Does anyone would help me tounderstand it?
Thx a lot!!