Let’s start with Swinburne’s description of Aquinas’ concept of a ‘miracle’:
Aquinas wrote that a ‘miracle’ in a wide sense is any event brought about by a rational agent in virtue of powers greater than normal human powers; and so many events brought about by demons or angels would count as miracles. But in a strict sense, he claims, a miracle is that which occurs outside the whole system of created nature; it is that which no other agent except God has the power to bring about. See Summa Theologiae, Ia.114.
(Existence of God, 2nd ed., from footnote on p.282)
1. ‘in a wide sense’
This is a good point: the word ‘miracle’ has more than one meaning; it is ambiguous.
In a ‘wide sense’ it does NOT imply the existence or involvement of God in the alleged event. But in a narrower sense, it does imply the existence and involvement of God. One obvious implication is that the following argument is ambiguous:
(1) Miracles have happened.
(2) God exists.
If ‘miracles’ is used in the narrower sense, then (1) does logically imply (2), but in that case (1) begs the question. To establish that a miracle (in this narrow sense) has happened, one must first establish that God exists.
On the other hand, if ‘miracles’ is used in the wider sense, then (1) does not logically imply (2), although it might be used as evidence in support of (2), but the reasoning would need significant expansion and explanation (as for example, the reasoning given by Swinburne in Chapter 12 of The Existence of God: “Arguments from History and Miracles”).
2. ‘in virtue of powers greater than normal human powers’
This seems to be a bit too broad; this makes too many kinds of events count as miracles.
Superman leaping a building in a single bound would count as a ‘miracle’ on this criterion. Space aliens who have spacecraft with the power of invisibility or that can levitate large trucks and airplanes would be performing ‘miracles’ when they use such advanced technology. Even world-class athletes and scholars and scientists (who may be said to possess ‘powers greater than normal human powers’) may sometimes perform miracles, when they exercise their rare abilities. But none of these seem to be examples of miracles, so this condition appears to be too broad.