674 ignite damage from a lone 543 fire blast crit. Bug or intended?

SO I've been playing around with a 0/10/21 FFB build for PvP, and I think ignite is interacting with some talent in the frost tree in an unexpected way. I've seen a few instances of getting a single crit with fireblast or LB, and then ignite (from no other source) dealing 600-700 damage. It feels like ignite is being modified by Ice Shards or something (though I've no idea why)?

Is there some intended interaction that I'm being blind to, or is this unintended?