I've heard that somewhere else also, but isn't the stadium brand new? How can it be small, especially for the Olympics, wouldn't that be a disqualifying thing for an Olympic venue?
The rink of Iceberg Palace in Sochi isn't small (30x60m), I think it is normal size. For example the Fukuoka rink and TEB rink are also 30x60. The Vancouver Olympic rink was slightly bigger (30x61).
I think Yuna had difficulties in adjusting her speed and jumps to the small rink in Zagreb. It was only 28m x 58m. The size of the rink can make a huge difference.