Are we starting sweet potato slips the hard way?

I'm definitely not an expert, I have only been growing sweet potatoes a couple of years. I have found it easiest for me to plant the sweet potato in a shallow pot. This is very easy, and produces lot of slips . I'm actually getting slips from the same sweet potato I used last year.  
I wanted to share slips, and didn't know the name of the sweet potato I started last year, so I started one in the house with a heat mat to get an early start. It's working great.
My daughter bought a couple of sweet potatoes to eat, and they were sitting on the table not far from the grow light. They are growing slips. It makes me wonder if the soil and watering isn't necessary.
You will see the pictures and say wow huge! difference, why is she even questioning the process? Keep in mind the one in the soil were on a heat mat, and have been planted for 6 or 8 weeks??? The volunteers haven't been on the table that long, so not fair comparing them.
One thing is for sure I will have plenty of sweet potato slips.

I start mine by taking a tuber and putting it in a milk carton, laying down, with a bit of soil, and then flooding it every so often. I do this outside== no mats or lights. if it were cold, I'd probably do it under a grow light in my office.
Just letting it sprout "au naturel" doesn't give you a lot of leaves, just leggy stem.

Hi Jen,

Thank you for sharing this comparison.
I am trying to grow slips and next sweet potatoes, but so far it failed somewhere. Your pictures got me thinking: At what length do you cut off the slips? I might have been doing this way too early.

Kind regards, Nynke

The general suggestion is 6 to 12 inches tall. I like the take the slips from the sides when they have 3 or 4 sets of true leaves. The side shoots often already have roots. Lots of people root the slips in water, but I think it's easier to just plant them in the place I want them to grow. That being said this year I got a very early start, so I have planted some slips in small pots until it's warm enough to plant outside. Time will tell if this is a good idea, or bad.
Good luck, and keep trying, you will find what works for you .

Thank you Jen,
than I have removed them way too early in the past. I will be more patient in the future, if a sweet potato will make leaves again ever...

I don't do much of anything. My bin of sweet potatoes just starts sprouting this time of year. (That may indicate that I'm bad at curing them.) I'll select a few good ones and set them aside soon, but no need for soil, water, or artificial light. Just break the slips off and stick them in the ground once they're big enough and we're expecting a few rainy days. I don't want many leaves on my slips — they just create water stress, in my view.