Since the object that information was required about (Ulamog) was not in the zone it was expected to be in when the trigger resolved, the game used last known information (LKI). That includes the kind and number of counters on it.

113.7a Once activated or triggered, an ability exists on the stack independently of its source.
Destruction or removal of the source after that time won’t affect the ability. Note that some
abilities cause a source to do something (for example, “This creature deals 1 damage to any
target”) rather than the ability doing anything directly. In these cases, any activated or triggered
ability that references information about the source for use while announcing an activated
ability or putting a triggered ability on the stack checks that information when the ability is put
onto the stack. Otherwise, it will check that information when it resolves. In both instances, if
the source is no longer in the zone it’s expected to be in at that time, its last known information
is used. The source can still perform the action even though it no longer exists.

608.2h If an effect requires information from the game (such as the number of creatures on the
battlefield), the answer is determined only once, when the effect is applied. If the effect requires
information from a specific object, including the source of the ability itself, the effect uses the
current information of that object if it’s in the public zone it was expected to be in; if it’s no
longer in that zone, or if the effect has moved it from a public zone to a hidden zone, the effect
uses the object’s last known information. See rule 113.7a. If an ability states that an object does
something, it’s the object as it exists—or as it most recently existed—that does it, not the
ability.