Disney has indicated the prices for Genie can vary. Is TP actually trying to 'forecast' the future prices?
I would first check on the official Disney website to see what prices are posted. No idea how far in advance they determine them since you can no longer buy Genie paid options ahead of time.
That week is school vacation week for public schools up here in Massachusetts. Same may be true for other areas. I know a lot of families that will be in Disney that week. I would expect it to be fairly busy.
It is an educated guess. Nobody knows what the price will be that day except Disney, and that may not be decided until a day before based on crowd size.
It's an estimate based on their crowd calendars. April 17 is the day after a runDisney race, so I think they predict the runners will stick around and lots of them will buy Genie+.