user78: From Lightning Network documentation:

Used in several of the BOLT documents to denote the genesis hash of a target
  blockchain. This allows nodes to create and reference channels on
  several blockchains. Nodes are to ignore any messages that reference a
  chain_hash that are unknown to them. Unlike bitcoin-cli, the hash is
  not reversed but is used directly.
For the main chain Bitcoin blockchain, the chain_hash value MUST be
  (encoded in hex):
  6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000.

However this wiki entry about Bitcoin's genesis block has 

GetHash()      =
  0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

Indeed, inputting the latter value into blockchain.info yields Block 0, while the former value cannot be found on blockchain.info.
Why does the value 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000 appear in Lightning Network as "Bitcoin's genesis hash"?

user76567: It is the same hash but reversed since bitcoin transmits data using little endian format (most significant byte last)

user5757: They're exactly the same number; one is written in little endian notation and the other is big endian.  Notice that the bytes (two-hex-digit pairs) are exactly reversed from one to the other.
Block explorers like blockchain.info usually expect big-endian for block hashes.  The proof-of-work requirement means that the most significant bits have to be zero, so big endian makes it easier to see this.

78: <p>From Lightning Network <a href="https://github.com/lightningnetwork/lightning-rfc/blob/master/00-introduction.md" rel="nofollow noreferrer">documentation</a>:</p>

<blockquote>
  <p>Used in several of the BOLT documents to denote the genesis hash of a target
  blockchain. This allows nodes to create and reference channels on
  several blockchains. Nodes are to ignore any messages that reference a
  chain_hash that are unknown to them. Unlike bitcoin-cli, the hash is
  not reversed but is used directly.</p>
  
  <p>For the main chain Bitcoin blockchain, the chain_hash value MUST be
  (encoded in hex):
  6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000.</p>
</blockquote>

<p>However this wiki entry about Bitcoin's <a href="https://en.bitcoin.it/wiki/Genesis_block" rel="nofollow noreferrer">genesis block</a> has </p>

<blockquote>
  <p>GetHash()      =
  0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f</p>
</blockquote>

<p>Indeed, inputting the latter value into blockchain.info yields <a href="https://blockchain.info/block-index/14849/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f" rel="nofollow noreferrer">Block 0</a>, while the former value cannot be found on blockchain.info.</p>

<p>Why does the value <code>6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000</code> appear in Lightning Network as "Bitcoin's genesis hash"?</p>
 76567: <p>It is the same hash but reversed since bitcoin transmits data using little endian format (most significant byte last)</p>
 5757: <p>They're exactly the same number; one is written in <a href="https://en.wikipedia.org/wiki/Endianness" rel="noreferrer">little endian</a> notation and the other is big endian.  Notice that the bytes (two-hex-digit pairs) are exactly reversed from one to the other.</p>

<p>Block explorers like blockchain.info usually expect big-endian for block hashes.  The proof-of-work requirement means that the <em>most</em> significant bits have to be zero, so big endian makes it easier to see this.</p>
