Why did my amp just crash and burn ?

Thankfully it was just a fuse and not the magic smoke!

I am so pleased your amp isn't damaged and working again.

Yes, lesson learned.  NEVER fiddle with speaker leads regardless of terminal type while the amp is live.

In fact don't fiddle with any leads while the system is up.

I don't like spade terminals but they are near ubiquitous now. including on my Martin Logan CLXs.  There is benefit in getting them as tight as possible, short of breaking the connector inside the speaker.  I recommend sticking to fingers and not using pliers etc.  I find they loosen over time and need re-tightening every now and then.

Now's the time to get another replacement fuse and put it where the other one was!

If the amp is totally dead then the mains fuse is most likely blown. You need to check after replacing the mains fuse that you have both channels working as it is possible that you may have blown the output stage of the channel on which the spades were adjusted. If that is the case then the amp will have to be looked at by a technician as, according to the manual, the amp does not have fuses on the output stage.

Glad to hear it was just the fuse. Many of us have learned the lesson the hard way, always turn power off when changing any type of interconnect or power cord.