For a heal to be generating aggro the source should be mentioned in log for the mob to gain aggro from it.
For example [20:42:11] Foyn's Manifestation of Regrowth heals you for 64.
Foyn builds tiny amount of aggro because the mob sees him as the source of heal.
When you tap, the source in combatlog is not mentioned. (Player name is needed for mob to modify the hate list)
In other words it's not you. Mob cannot see the source so there will be no aggro on hp tap.
[20:46:13] You are healed for 272 (health tap).