Spooky phone experience on Whats App - dilemma Pls help

I am pretty technology competent but I have had a really strange experience on my phone I just can't figure out.

At 0944 last night I got a Whats App message from my own mobile telephone number (came up as a my number but not my name) it included my profile picture. The spooky thing is that the message contained a video that was not on my phone. When I checked the video it was footage sent only to my mum on another phone earlier that day by my partner. So only my mum and partner had that video footage, no one else in the world. At first I did not recognise my number so I sent a message back saying who is this - it showed two blue ticks to indicate the message was read and it indicated the person was online - there was no reply.

My partner (who has not been in all day) and mum checked their phones and definitely 100% my partner had only sent the video to my mum (when not in the house) and she did not forward it to anyone.

The stranger thing is so when I change my profile picture on what's ap the profile picture on the erroneous message that contains the video also changes. This rules out it being from someone who has somehow managed to clone my number.

This whole situation has left me and mu my partner at a loss as to how this could have happened. We have gone through lots of theory's put none make any sense. The video footage was of a demonstration so even started thinking of conspiracy theories but still does not make sense.

Please help.