Not necessarily. With that 50mL of cake, you should have let the yeast (dead, alive) settle out, then decant most of the liquid and leave a little to create a slurry with the remaining yeast. Then add that to your cooled 1L of wort. Adding all that excess liquid isn't helping anything. I would say as little as 5mL of healthy yeast slurry could inoculate a 1L starter. It would just take longer to grow up.
You can't really overpitch with a 1L starter into a 5 gallon batch, unless the starter is unhealthy. Again, just make sure you decant off most of the liquid before you pitch the slurry.
Yeast growth will be limited to the amount of sugars available. So, if you added a very healthy and lively 50mL yeast [cake] slurry to 1L of starter, you might not get much benefit. You could probably have just added that 50mL to your 5 gallon batch.
