Random file names assigned to Live Photos after Airdrop

If I send live photos from my iPhone (XS, IOS 12.1.4) to my MacBook Air (OS 10.12.6) they arrive with a completely random set of numbers for their filenames, and not even in filename order.

i.e.:

3408

3409 (OK so far..)

7556

0007

2001

7816

7561

1524

2622

3698

1694

Mysteriously, I sent the photos again, and they arrived with the same numbers they'd been given on the first transfer. Is this AirDrop doing this? Or my phone?

When I check the same photos' EXIF data they have different numbers, not the ones they arrive with on the MacBook.

I spotted while checking this that these are Live Photos - is this the reason? And if so, what's going on?