WhatsApp grey ticks but message info says read?

[inappropriateportioncontrol]

If you long press a message you can click on an "I" icon at the top of the page.
This says "read ' but the ticks are still grey . Any explanation??

The person has their read notifications switched off so it will still show as grey even if they have read it

You can mark it as read without opening it when the message comes through from the phone home screen.
The options are reply and mark as read

O don't think they have notifications turned off , they are not tech savvy and the trucks do eventually turn blue. I'm ,100% certain that they are not turning notifications on and off .
Must be as @Christmasbird has said

Although I can't see those options on my phone.