I call shenanigans. The researcher wrote the name of each toy onto it with a Sharpie - clearly the dog simply read the name off instead of memorizing all 1000 items.
I think it's funny that the dog's recall outpaced the researcher...
The article mentions the fact that humans can use context to help remember words, but the dog has to use rote repetition. It's interesting that the reliance on context that helps us learn stuff in general could mean that dogs may actually be "better" at building a vocabulary of 1000+ unrelated names.
There's just so much sloppy research out there.