没有什么实质上的区别
as a matter of fact = in fact,“事实上；实际上”,在句中作插入语,
例如： As a matter of fact,I do know her.
事实上,我的确认识她.
He appears to be strong and healthy,but,as a matter of fact,he suffers a very weak heart.
他外表显得健康结实,事实上,他的心脏很衰弱.