I was shut down in my last gaming session when the WE player claimed that any flying unit must use it's land speed in order to charge a unit that is in a forest, unless of course they have forest strider. I cannot seem to find a reference to this rule in the main book. The Internets has threads agreeing with both sides, neither of which provide any justification for their rulings.
terradons and razordons have strider. (only fliers to have this as far as I know) Ps. I think that rule is under fling units somewhere. Pps. there is definitely a general rule that fliers (without strider) can't land in terrain.
The only restriction for where flyers can land, from page 71, "It may not finish the move on top of another unit or in impassable terrain." There is no restriction on forests in the flyer rule section and forests are not impassable. I can find no rule in the terrain section forbidding flyers landing or charging into forests, but it does say that, on page 119, "Models with the flyer special rule that begin or end a flying move in a forest must take a dangerous terrain test". Again nothing forbidding flyers to go into a forest, but a dangerous terrain test must be taken. Terradons have the forest strider special rule so would not in fact have to take this dangerous terrain test. Ripperdactyls do not have have the forest strider special rule so would have to take the dangerous terrain test. I don't see how this is open to interpretation in all honesty. If they push it again you have to ask them to find the rule in the rulebook saying you can't do it and you can point out these two pages to them.
I 100% concur with bugleboy. Good post, sir. The OP's opponent may be referencing old rules. I know from memory that under 6th Ed., that opponent would be very correct that land movement would have to be used. I don't remember 7th Ed. rules how it worked, but it wouldn't surprise me if it was the same restriction in 7th Ed. as in 6th Ed. Make sure your opponent is using 8th Ed. rules! Ol' grognards have trouble adjusting to new edition basic rules and commonly flub which rules apply to the game system being played. I know I made uncountable mistakes at the 6th/7th Ed. transition...and, once again, numerous flubs at the 7th/8th Ed. transition. You should research after each game to find the answers to rules questions that arose during play. Always strive to implement the current rules better than the last game played and you'll be fine; you just need to have fun playing the game as best you can.
You do have the option of using the model's movement value for charging from/into a forest to avoid the dangerous terrain test. But that's often a 2 instead of a 10 to add to your charge distance. Keep in mind that you still get swiftstride if you choose to use the models M value...