Encased in ice - yes.
Turned to mush - in subzero ( centigrade ) temp - not likely
Mush having lower liquid temp than ice? No no & NO !
Whatever - the pic is nice.
From the article:
"the temperature provided the perfect recipe: it was cold enough for the ice to remain, but warm enough for the apples to turn to complete mush, since apples have a lower freezing point than water."
And yes that's possible, it's the principle behind those first aid ice-packs: It's water and
starch.
When they DO freeze they they're colder than plain ice and take longer to become liquid.
Same principle explains seawater not freezing until about 28 degrees F but in that case it's the salt..