Technically truncate is a fully logged operation. Minimally logged means that there is a difference in logging behaviour between bulk-logged/simple and full recovery and that in bulk-logged and simple recovery models the operation logs only enough for a roll back, not enough for a roll forward operation, such an operation flips the appropriate bit in the ML map and results in the next log backup copying the affected extents into the log backup.

Minimally logged does not mean that only the page allocation/deallocations are logged. Many operations, including truncate table, drop table, drop index, select into, insert into, alter index .. rebuild, log only page allocations/deallocations in all recovery models.