Was Trinity Force proc changed to a crit?

Could be the spell blade hitting you, could be the extra crit chance they get from it causing them to crit you as well.

It wasn't changed to a crit. Though, they may have decided to use the critical strike font to emphasis the spellblade proc, similar to Karthus's single target Q.

Spellblade proc cannot crit, but the crit icon will show if your AA has crit.