I can't really tell anything from the pic of all of them, but as far as the pic of the one alone--sorry to say, but it looks nothing like a Yorkie. Yes, running off for only 30 minutes would have given her PLENTY of time to find another pal. You will need to have these pups and the father DNA'd to determine which, if any of them, he actually sired. As others have already pointed out, it is possible for her to have carried a litter that was multi-sired.
Also, the size of the parents alone is not necessarily an indicator of what size their offspring will be. You have to take into consideration the size of all the dogs in their line, not just the size of the dam and sire. But I'm sure, as a breeder who I'm sure thoroughly researched genetics and breeding first, you were already aware of that.
