This looks like a simple mistake of poorly chosen words. In the sentence right before the infinite rise time comment, he notes "Intuitively, the steeper the signal’s rise and fall time, the less influence random noise has in the time domain."
Had he said "the steeper the signals' rising and falling edges" instead, the statement would have been correct and much clearer. I understood what he meant, even if he didn't quite say it correctly.
it may be that to make the signal traverses the decision threshold (vt) instantaneously, in the ideal case you are referring to, both rise and fall times should be zero (not infinite).
Elio P. Balsamo
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Are the design challenges the same as with embedded systems, but with a little developer- and IT-skills added in? What do engineers need to know? Rick Merritt talks with two experts about the tools and best options for designing IoT devices in 2016. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.