Sometimes things on Tibia do not work as most of players would think or assume (it may be even unintended by the devs sometimes). You have made a small lecture regarding summons and also showed an evidence based on what most of people would think, which is interesting. But a solid test is something that could show other results.
Summons can work in an unexpected way. For example, not so long ago, a player convincing a wasp could potentially get a skull if the wasp poisoned a character before. People would kill the poisoned character by the wasp and would go after the player who convinced the wasp (as you can see, a trap that could potentially cause a red skull on someone). The convinced beast (something that you consider equivalent to a summon, as it is written on your first sentence) on this case was already an "extension" of the character after convinced, but it didn't matter at all, since the damage made by the convinced creature before would count now as something related to the player.
The "ashes" are actually pretty similar to the remnants that a fire elemental corpse displays after dying. I remember it because I used to summon a lot of Orc Berserks in the past, and once they were killed, they would turn into this and soon after would vanish (and now they just puff)