The interpretation timeline
Mark 6:49 Douay-Rheims

But they seeing him walking upon the sea, thought it was an apparition, and they cried out.

A.D. 430 – 1832 3 witnesses

Patristic

before A.D. 750
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“(de Con. Evan. 2. 47) But how could they understand this, except from His going a different way, wishing to pass them as strangers; for they were so far from recognising Him, as to take Him for a spirit. For it goes on: But when they saw him walking upon the sea, they supposed it had been a spirit, and cried out.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“For they all saw him, and were troubled,.... Had it been only seen by one, it might have been thought a fancy, and the effect of mere imagination; but as every one saw it, it was out of all doubt that so it was, and which gave them the greater concern: and immediately he talked with them; as soon as they saw him, "that very moment", as the Syriac renders it; that so by hearing his voice their fears might be allayed: and saith unto them, be of good cheer, it is I, be not afraid; See Gill on Mat 14:27.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“They supposed it had been a spirit - That is, by whom the storm had been raised.”
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.