IT ISN’T SQUIRREL-TURTLE.
IT’S ‘SQUIRT‘-TURTLE. Squirt. I.e, squirt water AND squirt meaning littlest.
THE ‘RANDOM SQUIRREL TAIL’ IS MEANT TO LOOK LIKE WATER. Like, a spout/squirt of water curling over.

PLUS, if it WAS a squirrel tail, what’s it got to do with Squirtle? What’s a squirrel got to do with a water turtle, AND WHY WOULD WARTORTLE HAVE IT TOO?
WARTORTLE HAS NO REMNANT OF THE WORD/NAME ‘squirrel’.