I thought his method of multiplexing the single channel was very smart. I guess it's more common on 2 channel or high end 4 channel scopes to have a dedicated trigger input, which I've checked this one doesn't have. That said, there're digital inputs that could've been used. Presumably from whatever was controlling the laser.
Frankly it's uncommon to not have a trigger input. I'm not sure I've ever seen a DSO in person without a trigger in.
I was confused by that part of the video exactly because I wondered why he wasn’t using the trigger input. Or, would it normally be possible to use a different channel as the trigger for the first channel?
He explained that. His inexpensive oscilloscope _can_ trigger from the second channel, but only at one billion samples per second. Where’s the fun in that?