Maybe he's suggesting that a private purchaser would be outbid because of a tax advantage that the land-trust has. But someone putting land into a trust already suffers the loss of much of its possible use in development, so it's not that much of an advantage.
Frankly, there's a lot that's voluntary about the landtrusts that make it more appealing than the standard condemn-and-seize eminent domain operations. At least there's some private control, and sometimes the land becomes available for recreational use, improving the values of private pty nearby.
Watched a waterfall area in NC go through some scary weirdness. First the state didn't bid enough on the property, then tried to seize the property later from the owner without paying him FMV for it. The owner had already deeded much of the scenic part of the land for **public** enjoyment, a gift! Didn't keep up with what eventually happened...