Spurt: a short, sudden burst. A short spray of water from a garden hose could be a "spurt". We use the phrase "growth spurt" to describe when a child grows tall

Spurt: a short, sudden burst. A short spray of water from a garden hose could be a "spurt". We use the phrase "growth spurt" to describe when a child grows taller in a short time. They're using it to describe a short, relatively large transfer of accumulated data collected while the wifi connection is deactivated, and transferred in a sudden stream when it's turned on.