The Rising and "gain pool"

Hi

Last night I played The Rising and we wondered what was defined as "gain pool". I have a MTG background so for me, any effect that raises your life total, even setting it to an amount bigget that the amount you had, is life gain. On the other hand, my friend told me moving was different from gaining. i checked for some clarification bu I couldn't find any.

Many thanks in advance and sorry if it seems an obvious question

Rising, The
[Event] Event

Gehenna. Do not replace until your prey is ousted.
Requires at least two other Gehenna cards in play. A Methuselah cannot gain pool during his or her own turn unless he or she has the Edge or at least one victory point. Any pool he or she would gain goes to the bank instead.

And what about Vessels, blood dools, and all related cards? Or transfers from the uncontrolled region to your pool.

They all change your pool total in the positive direction, thus are considered to be gaining pool. You may move the blood, with the result that it disappears into the blood bank.