This OR operation determines which type of AT command is subscribed to. So for example, if you have:
adl_atCmdSubscribe( "AT+CUSTOMER", ATCmdCustomer_Handler, ADL_CMD_TYPE_READ );
the callback function will only be called if you send the read command (AT+CUSTOMER?), and the Params->Type variable will be set to ADL_CMD_TYPE_READ. If you send anything else, you will receive an error.
Another example, if you have
adl_atCmdSubscribe( "AT+CUSTOMER", ATCmdCustomer_Handler, ADL_CMD_TYPE_READ | ADL_CMD_TYPE_PARA | 0x11 );
the callback function will be called on a read command (AT+CUSTOMER?) and a parameter command with at least one parameter and at most one parameter (AT+CUSTOMER=1). Any other type will return error (for example, AT+CUSTOMER=? or AT+CUSTOMER=1,2).
So in your example, the callback function will be called on a read command, a test command and a parameter command. The command type provided in the callback function (Params->Type), for example
void ATCmdCustomer_Handler (adl_atCmdPreParser_t * Params)
will depend on what command you send.