You're a god damn genius, OP.

Pat yourself on the back, you've done your kind deed for the day. 5+ is cat lady territory, now she's just borderline. Phew!

How don't you know how many cats your friend has when you're asked to take care of them for a while? Really. And maybe know how they look like?

I hate u cat lovers They are stupid creatures. So please get a dog instead

TBH, the most logical conclusion I can come up with as to why the OP thought that specific cat was the stray is probably that she HAS been to her friend's house before and every time has only ever seen four cats (the ones she fed) because the one under the sofa maybe always likes to be under sofas or cupboards or whatever due to being shy or something. She never saw it so she thought her friend only ever had the four recognisable ones. That's the only logical explanation I can think of. If she knew this friend for a long time and her friend didn't tell her about the fifth cat (or took it in recently wthout telling) her actions are SLIGHTLY less condemnable. Slightly. I still would have checked first, and rather than kicking it out I probably would have brought it to the pound or whatever. Someone made a good point that if it WAS a stray, the other four cats being the territorial bitches they are would probably shown their aversion to the fifth cat when OP brought it out from under the sofa or whatever. OP is kind of stupid/careless, but at least I think I understand why she may have thought there were only four cats.

You really made the assumption that a cat that was INSIDE the house didn't live there?

What??...why?....how on earth did you come to the conclusion that it was a stray? Was the idea of having 5 cats instead of 4 too much for you to fathom? I can't even...

Why on earth would you kick an animal out of someone's house? You're the animal here OP.

Why would you think it's a stray?! How many people randomly have cats in their house... Especially if they have four! You should have fed it and if it was a stray she would probably add it to the mix anyways!

Who kicks a cat into the street even if it is a stray?? Jerk.