Its hard to tell, but it looks your spine flexes a little during the movement.
As for toro's question, they are very very similar. Both are a hip dominated movement...neither (when done correctly) should involve spinal flexion to extension.
Here's a couple videos.
The first one is great form and a good explanation...and as an added bonus, the instructor is quite attractive
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The second one is a graphic representation of the action of the hamstrings as the primary mover during the lift:
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Notice around 30 sec in that the spinal erectors maintain an isometric hold (do not shorten) to prevent spinal flexion. Notice how the hamstrings do get stretched as the hip flexes and the ishium travels upwards.
Now, around 40 seconds you get to see what happens when there is either a lack of flexibility or if flexion occurs in the spine. Notice with spinal flexion the ishium does not travel upwards, the hamstrings do not get stretched (ie. are not fully recruited), and how...just plain ugly...the movement looks.
Br