I'm assuming that the students were - given the physical location of the sign and their comments about the Lawn itself, the police officer's being there, etc. - and I would assume that Ryan would be at or near UVa as well. Figured that, while not certain, it would be a small enough chance not to really be worth going into.

Per the Honor Committee

“Lying” shall mean the misrepresentation of one or more facts in order to gain a benefit or harm another person, where the actor knows or should know that the misrepresentation will be relied upon by another person.

Absent any further context (like if they started the Zoom call by pressing a button on their phone and setting it down in view of President Ryan), I'd think that using a physical recording device to (presumably) avoid Zoom's informing someone that they're being recorded would count as a "misrepresentation of one or more facts", and the fact that they've released the conversation seems to provide the benefit/harm aspect.