No. That is not what he is saying. Import tax is due on used boats also, so long as they were not originally manufactured in North America.
Check with the border. They will give you whatever is their current protocal.
I know nothng about taxes when going from Canada to US. Going the other way, the Canadian rules use the same mushy words that fail to tell you whether the rules apply to used boats or cars. On Motorhomes the rules clearly state the age, as it is important to them, and over a certain age, admissibility rules change.
For cars and boats, however, according to a reasoned interpretation of the rules, a dinghy mfg in Venezuela with a motor mfg in Japan ought to have attracted 6%. then GST, then PST. I was actually asked to pay only GST at the border, with PST left to the Provincial Gov to collect on registration. Because I was importing from a NAFTA partner, the US, where duty was already paid, I was not asked to pay it again.
For a car mfg in Germany, again I expected to pay duty of 6% GST of 5% and PST of 7%. At the border I was asked to pay only GST, at insurance and safety inspection time I was asked for PST. Because the car wasn't new, and duty had been paid to a NAFTA partner upon its arrival in the US, I was not asked for Duty.