Hi there,
not sure if they used a plugin, but its just HTML using the unsemantic grid which GP includes a stripped down version. So this markup could be used to create those rows:
<div class="my-section">
<div class="grid-container">
<div class="grid-15">
<p>Col 15%</p>
</div>
<div class="grid-30">
<p>Col 30%</p>
</div>
<div class="grid-25">
<p>Col 35%</p>
</div>
<div class="grid-30">
<p>Col 30%</p>
</div>
</div>
</div>
You can then use the my-section
class ( which you can name whatever you want ) to style them.