No its probably the novelty of seeing a smaller dog. The over excited behavior of the min pin probably didn't help much either.
If batman doesn't mind being around dogs his size then thats a start, I would suggest you allow him to socialize with dogs his size first, then introduce a calm smaller dog. Every now and then give him treats so that he associates the meeting to something good.
Also watch your own body language. If you are holding in your breath, have a tight hold on the leash, or doing anything that might otherwise communicate that you are uneasy then your dog will also become uneasy and react in a similar manner of the one you just described. (although this time it probably wasn't your fault).
Also instead of having them meet face to face (which is not a canine thing to do anyway), have them meet while both of you are walking. Let them sniff each other, give them a treat and be on your way together (so that they both get to explore with eachother and start to feel more comfortable around each other.
Thats all the advice I have for now, hope it helps!