It's similar to the term dynasty. For some reason the overuse of the word dynasty drives me nuts, but generational doesn't. I guess there could be a better word to use that more accurately characterizes the type of prospect Bedard is, but I guess its being used to describe the highest level of elite prospect, a surefire cornerstone star player. Someone who is regarded higher than a normal number 1 overall pick. To put it in basketball terms because I'm more familiar with prospects there are a few different tiers:
Tier 1: LeBron - Generational, no doubt prospect. Expected to be a cornerstone of the league moving forward
Tier 2: KAT/AD/Kyrie - Likely superstar and among best players in the league for the duration of career
Tier 3: Wiggins/Ayton - High floor player with superstar upside but maybe a little more risky in terms of career projection
Tier 4: Anthony Bennett - There's probably a tier between these (maybe a Joe Smith tier) but very high risk player with higher bust potential. Is going number 1 because its a poor draft and someone has to be drafted 1st.
(I realize this is obvious to many here, I just wanted to spell it out for my own good)
Bedard is a Tier 1 prospect similar to McDavid or Crosby. Kane was probably a Tier 2 prospect but rose to a league cornerstone type of player.