Another way would be:
$post = $content->comments(1,0);
The IPS\forums\Topic object model has the following core method on it:
* Get comments
* @param int|NULL $limit The number to get (NULL to use static::getCommentsPerPage())
* @param int|NULL $offset The number to start at (NULL to examine \IPS\Request::i()->page)
* @param string $order The column to order by
* @param string $orderDirection "asc" or "desc"
* @param \IPS\Member|NULL $member If specified, will only get comments by that member
* @param bool|NULL $includeHiddenComments Include hidden comments or not? NULL to base of currently logged in member's permissions
* @param \IPS\DateTime|NULL $cutoff If an \IPS\DateTime object is provided, only comments posted AFTER that date will be included
* @param mixed $extraWhereClause Additional where clause(s) (see \IPS\Db::build for details)
* @param bool|NULL $bypassCache Used in cases where comments may have already been loaded i.e. splitting comments on an item.
* @param bool $includeDeleted Include Deleted Content
* @param bool|NULL $canViewWarn TRUE to include Warning information, NULL to determine automatically based on moderator permissions.
* @return array|NULL|\IPS\Content\Comment If $limit is 1, will return \IPS\Content\Comment or NULL for no results. For any other number, will return an array.
public function comments( $limit=NULL, $offset=NULL, $order='date', $orderDirection='asc', $member=NULL, $includeHiddenComments=NULL, $cutoff=NULL, $extraWhereClause=NULL, $bypassCache=FALSE, $includeDeleted=FALSE, $canViewWarn=NULL )