Haha, this is awesome, I had something similar happen with guppies.
I have about six guppies total two of which are Cobra Guppies, that were added later than the others and were much smaller.
About 2 weeks after adding the cobra guppies I started a new 29 gallon tank and had eventually moved all the guppies in there with 5 Neon tetras. Since the very first day the smallest cobra guppy showed interest in the tetras and now he will "play" with the guppies (that are constantly goofing off in the tank) half the time and then will randomly leave the guppy herd and start swimming around with the tetras. He's not picky, he just likes variation I guess