2009 Suzuki LS650 Battery Problem/Question

I bought a new battery that had the same amp and voltage as my current battery that I was going to replace. I double checked via the website, and they confirmed it would fit my motorcycle. (Moto Classic YTX14AHL Sealed AGM Battery)
Since this would be the first time I replaced a motorcycle battery, I simply unhooked, took out, and re-hooked up my old battery. No problems. The old battery was a NAPA Power Sport Legend Premium AGM 12 Volts 220 CCA. When my new battery came in, I disconnected the old battery (negative first, then positive).

When I examined the new battery, the terminals were slightly different. Instead of the screws fitting into the terminals, you had to use the little block bolt below to screw it tight. I connected the positive side, then went to connect the negative side.

AFTER I had finished screwing the negative terminal on and I was standing back up, the battery terminals erupted into flames. This being very unexpected, I went and grabbed a water bucket (I know, not smart, but I was just thinking “FIRE!”) I put the fire out pretty easily, and then proceeded to carefully unscrew the negative terminal and soon after removed the battery. Battery looks PERFECTLY fine, (I even went to get it tested at Autozone later and it tested good). The positive terminal’s rubber covering was charred, as well as where the negative wire was beside the battery. The battery box was slightly “melted” near the positive side, but other than that, no damage.

After asking a few of my motorcycle buds, google, and an Autozone employee who works on motorcycles, I came up with nothing…. besides “well you must have hooked the terminals backwards” or “something metal must have been creating a short.”

After regaining my courage, I did some extra covering on the wires with electrical tape (they weren’t bare, just a little charred), then took the OLD battery and did the same exact process, no problem. The fire/craziness from the previous battery apparently didn’t blow any fuses, and she cranked right up.
WHAT IS GOING ON???? I know I will need to replace the battery eventually, but I am terrified to try it again. Thanks for your input!