Question about re-entry/becoming UFA

The June 1 deadline for teams to sign some of their prospects has passed, and I am confused over one aspect of this.

Why is it that, had the Penguins not signed Maxime Talbot by June 1, he would have re-entered the draft this year, yet

R.J. Umberger became an UFA after he did not come to terms with the NY Rangers?

What is the difference between these two situations? Does it have do with RJ sitting out a year, or because Maxime played in Juniors, while RJ played college?

Thanks for bearing with my ignorance.

 

in umberger's case it is because of his age. any north american over the age of 20 is no longer draft eligible, so he becomes a free agent cause he can't re-enter the draft.

 

for a little more clarification, for at least Major Juniors. If the player turns 21 before the end of the year (born before December 31st, 1983), then he is a UFA. If his birthday is after December 31st , 1983, he re-enters the draft.
I'm not sure how that worked with Umberger because he was in college and also 19 when he was drafted