Once again lets read what has actually been quoted. Tim Clark is expressing doubt about the Malaysian Government's statements about the incident:
While his doubts about the southerly track flown by MH370 are probably not widely held anymore, the integrity of the Malaysian Government, its state owned carrier, and its aviation authorities, in relation to the statements they made and the actions they took from day one ( 8 March) of the disappearance of the Kuala Lumpur-Beijing flight and its 239 passengers have already been destroyed from within.
It seems to be suggesting that he has accepted that it flew the southerly route. If, as the worlds largest operator of B777's, had any concern about the ability of the 777 and its crew to cope with a cargo fire and not disappear then why doesn't he ground the fleet until hard evidence of what happened is available?