A cutting disk of that size would need to be mandrel mounted.. (Mandrel = axle and hub).
4mm wide and 60cm diameter would tear itself apart under centrifugal force.
Even a flat sided disc cutter, without mandrel, would leave a quarter circle cut at the top and bottom of the overall cut.
The only other thing I can think of is a router, but that would have to have a prohibitively long length to diameter ratio.
Bend and break.
Can't get a saw in there because the ends of the cut are blind..
It looks like a saw cut but it can't be..
I don't know ??
It obviously caught the attention of the Russian guy.