Any trees under water did NOT grow there
you've never been to florida, have you? we have these wonderful things called mangrove trees. they grow underwater, in mangrove swamps.
not to say the point was valid or anything.
but anyhow. evidence for A flood is not evidence for THE flood. we have many examples of fossil beds created by catastrophe and sudden, massive floods. flood fossils look a certain way. they're usually arranged in large jumbles. it often takes a lot of work to separate animals of different species, let alone different individuals. broken bones (unhealed before death) are VERY common.
do fossils form underwater? yes. of course. what about all the trilobites? it just takes being buried under sediment, with enough pressure, and the right conditions. water is usually the agent that replaces the organic material with minerals.