How did a random trainer catch me while i'm surfing?

Question

That trainer wasn't a Swimmer though, I was surfing just to skip that fight but somehow they caught me and started walking on water. Is that some sort of glitch?

Comments

It was a female Ace Trainer though.

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Where was this?

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Undella Bay.

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The only female Ace Trainer in Undella Bay is standing in shallow water, which you can walk in.

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Yeah. (filler)

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So... what's the problem? Are you sure it was actually walking on the water you're not supposed to be able to walk on?

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Yes. (filler)

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You either saw something wrong or a glitch occurred for some reason, then.

Answer 1

Yes, this is a glitch.

When the player enters the sight range of Ace Trainer Summer in Undella Bay from the north while surfing, she will walk over water and challenge the player to a battle.

Source