can we not then classify or tag casting lots and drawing straws, as a kind of gambling activity?
No, since there is no bet put on the result and there is no gain.
Gambling means to put down money for a bet with the risk of losing it or gaining an amount out of this action.
In the casting of lots that are referred to in the bible, there is only a ay to randomly address things without a human decision and take it as the will of god, so two persons fore example draw lots and the one that is elected will either get the position or the task that is to be done.