The numbers of the Trollocs were certain sufficient to kill all the Tinkers. IMO, the Shadow's fear to present Shadowspawn to the Seanchan is also somewhat overrated. After all, the Seanchan already learned that a Forsaken stayed with Tuon. And in the end, this attack didn't convince the Seanchan to unite with Rand. If the Shadow saw an advantage in attacking the Tinkers (and as I said in a post below, it would probably be linked to the belief and order give strength-tactic, which Herid Fel developed), it would certainly be done.

We will see if this was just a random attack, or if there was more behind it. If my idea is true, we can expect further attacks on the Tinkers.