Is this supposed to be a joke? If it is, it's not funny. If some people took it seriously, they are likely to damage their motherboards permanently.
That's an oooold motherboard, probably from the Pentium 1 era. ISA slots, for heaven's sake. Heck, the guy doesn't even know how to remove a BIOS battery properly.
Any liquid on a finished electronics product, especially something as sensitive as a CMOS-based motherboard, is potentially disastrous. It may not cause damage IF it is perfectly dried out quickly, but getting it completely dry again is not as easy as you may think.
Blowing on it with a hair dryer for a few seconds will NOT do the job. There are hundreds of tiny spaces where water will remain unless the motherboard is left in a heated vacuum chamber, or out in the sun for days. It will cause corrosion and short circuits.
The person who posted it on YouTube probably meant it to be funny. But posting it here without a clear warning is in bad taste.