ebay parcel shop return problem

se2020

Sold a low value item on ebay.
Postage address was an "Argos in Sainsburys"
Put the eCP as part of the address. 

Have had no contact from buyer but had a return notification via ebay.
No reason given for the return other than "PUDO RETURN" In the comments section.

Google suggested this was due to the buyer failing to collect the item rather than actually wanting to return it for a refund.

I have received back a pair of shoes today (I sent out a pack of marker pens).
Haven't opened them yet but it's the correct tracking number shown in the return.

I suppose its possible that the shoes are worth less than the £7.49 pens I sent and the buyer is trying to scam me but I think its more likely that it's either some sort of mix up in Argos or the buyer has tried to return the shoes but send them back to the wrong seller?

ebay is telling me that I have received the return and to refund within 2 days.

I haven't messaged the buyer yet as I don't really want to get involved in posting these shoes around etc.

Do I just use the ebay option to report a problem and say the buyer has not sent back the original item?
Or contact the buyer and see if they know what's going on?