Tishana’s Tidebinder ETB ability targets an ability, not a permanent. However my opponent successfully prevented Tishana’s ability using Snakeskin Vail

Here’s what happened:

On my opponents turn, their Tia Lockhart’s landfall ability triggered.
While Tia’s triggered ability was on the stack I played Tishana’s Tidebinder.
Tishana resolved and its ETB ability went on the stack.
In response ( with both abilities still on the stack) opponent played snakeskin vail to give Tia Lockhart hexproof.
Snakeskin resolved.
Then with Tishana’s ability, I targeted the landfall ability.

But Tia Lockheart did not lose its ability. It kept its landfall ability and went on to win