Only way to know is to confirm with the actual seller. When the site says "supported" it can mean 1) supported out-of-the-box; or 2) supported IF with an updated BIOS.
If the actual motherboard you will receive was manufactured prior to the release of Kaby Lake, then, you would need a Skylake CPU just to update the mobo's BIOS. If the actual motherboard you will receive was manufactured after the release of Kaby Lake, then, there is a *chance* (not yet certain), that its BIOS *may* (or may not) be updated for Kaby Lake CPUs already.
To eliminate this issues or hassles, just get a B250M ITX motherboard.
PCPartPicker part list /
Price breakdown by merchant
Motherboard: MSI B250I PRO Mini ITX LGA1151 Motherboard ($89.99 @ B&H)
Total: $89.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-20 05:54 EDT-0400