Isbeau, I agree. It's odd to cut the yarn. I'd strongly prefer just to work across the stitches to the edge for the heel flap.
I'm very aware of any knots put into a sock - especially below the ankle. Blisters are not fun and should be avoided whenever reasonably possible. Cutting - tying-off - tying back on in a new place gives you 2 knots. Not just one.
But I've knitted socks since childhood... CindyS is new to the project. So by all means, follow this one particular pattern. But do be aware that it's not the norm for knitting quality, long-lasting socks.
BTW, CindyS, good for you for conquering sock-knitting! You are hereby officially deemed.... no longer a beginning knitter!
Long Knit CindyS - Knitter Extraordinaire!