When stimulating the GSpot, some woman have this effect. It can be referred to as female ejaculation, or porn still usually call is "gushing" or "squirting."
It's NOT urine. It is a clear fluid (that shares qualities with urine, like alkalinity) that is produced by the Skene's gland (very close to the urethra). A lot of women mistake it for urine when it happens. Actually, this is a fairly new thing accepted by the medical community. Notice how there is not a name for the fluid (doctor's haven't gotten that far, apparently!).
To me this seems like calling the female sexual desires hysteria, but that is another discussion entirely...
You're normal...it's fine...and you didn't pee.