It probably was done with a straight spiral bit in a CNC router. The bit would be relatively small (1/2" 12.5mm or less) and the curves would be made by machine motion. Why? Looks rather mass-produced, which leads there in the current era.
You can do the same thing without a CNC router by making a template, clamping it or sticking it to the blank sheet, and following the template, either with a router collar or a template-follower bit. Your template for the many slots would be one slot, and a way to index the next slot on the slot you just cut, not replicating all the slots (unless you are trying for "not big enough to buy a CNC" factory production.)
Likewise you can make one big curve template for the upper cut, then use it to make a template with two big curves at the correct spacing, and just measure to put that template the correct distance from the one you cut first. It's worth indexing to cut lots of parallel slots. For two cutouts on the top, measuring will be faster than creating a way to index the template.