A longer one would be nice, but I'd actually be comfortable calling that atrial fibrillation, especially if there are no discernable p-waves in any of the leads. It's irregularly irregular without any discernable p-wave.
I trust you already know all of this, I'm just posting this for everyone. Sinus arrhythmia has pattern where it speeds up when the patient inhales and slows down when they exhale (cause of the Bainbridge reflex, I just learned that from another post somewhere on here). I don't see this slowing down or speeding up.
I know a lot of people like to be pro ECG interpretators and cover up/fold over what the monitor says, but I believe the monitor often sees things better than we do (eg the QTc, PRi, axis, etc.). I like to use the monitor values/interpretation if it makes sense. If it's irregularly irregular, you can't see any discernable p-waves in any lead, the monitor couldn't see any p-waves to calculate the PRi, there isn't a lot of artifacts, and it's conclusion was atrial fibrillation, I would trust it.
Also cause it was so fast earlier (not on the strip), 160 or something, I'd say atrial fibrillation is more likely.