So was it due to adding more CO2, or was it due to the increase in lighting?

Why do you think that the pearling and good growth only lasted 2 days?
You ran out of something. It was not light and does not sound like it was CO2 either.

NO3
PO4
K+
Traces
Ca/Mg

See the EI article, it makes adding these very easy and rules out deficiencies as well as excesses in a couple of very simple steps anyone can do and does not require testing or chemistry knowledge.

Tell me the tank size, I'll tell you what to add and how frequently.
Ideally, after a large water change, there is a lot of pearling and you should try and see if you can attain that same growth and pearling all week long.

If it backs off a tad, that's okay, but the tank should pearl good most of week and after 1-4 hours if you use higher light/CO2 etc.

Riccia is a good indicator plant for pearling also.

Regards,
Tom Barr