Yes, the truck is an absolute myth and has no relation to Mew whatsoever.
In Yellow, you capture Mew using the "trainer fly" technique, which is a glitch in the game where you hold the start menu as you're about to fight a trainer, then Teleport just before he can walk up to you (the exclamation mark still appears). The trainer battle is still pending but you're no longer in the area after teleporting to the last Pokemon Centre, which disables your start menu and you must then battle a trainer whose special stat corresponds to the Pokemon you wish to obtain.
This glitch is performed using two trainers north of Cerulean and you catch Mew around that area too.
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