A DHT is a key-value store distributed across a number of nodes in a network. The keys are distributed among nodes with a deterministic algorithm. Each node is responsible for a portion of the hash table. A routing algorithm allows to perform requests in the hash table without knowing every node of the network.
In a blockchain, each node of the network stores the full data, so it is absolutely not the same idea as the DHT in which data are divided among nodes. Each new entry in the blockchain must be validated by mining. This process ensures consensus of the data.
The two structures are both distributed data structures but serve different purposes. Distributed Hashtable Technology aims to provide an efficient (in term of lookup time and storage footprint) structure to divide data on a network and blockchain aims to provide a tamper-proof data structure.