I am quite confident (but could be wrong, of course) that no homo sapien
existed 5.5 million years ago. Thus any boat building would have to be
done by some other primate.
I believe Glenn argues that there could have been preflood technologies
which were obliterated in the flood, and the population after the flood
was so small that an technological knowledge remembered by Noah and his
descendent would be of very limited practical use - and hence largely
forgotten in later generations. (Imagine what would happen if the totality
of all humans were reduced to a dozen or so people. Could they build
cars, planes etc.? Not likely - even if they were all engineers.)
Gordie