Accepting anything in dreams

Okay, so I found out about lucid dreaming about 2 weeks ago and introduced it to my roommate about 3 days ago. One day he told me he had a dream about a friend 2 years ago. They were hanging out at the friend's house and his brother, playing the Xbox and whatnot. Now here's the kicker. His friend is an only child in real life, but while dreaming, he easily accepts it as it's completely normal. After waking up, of course, he realizes that his dream makes no sense.

Why is it that he can't realize this in the dream? And what can he do to realize this if a similar case were to happen?

It's perfectly normal.

Our Brains, while we are dreaming, accept pretty much anything, I could go In-depth, but that it's late and I'm too lazy to. If it's keeping him from going lucid, if that is your matter, he has to "train" his brain to recognize these little signals or signs so that he can ultimately become lucid.

On a Completely unrelated matter: A lot of people make new accounts, yet don't even introduce themselves, sometimes they don't even stay at all.

Sleeping and dreaming turns off the prefrontal cortex. The prefrontal cortex is responsible differentiating between things like right and wrong, good and bad, and conflicting thoughts among others. Basically as we're asleep, we're more than likely to accept something like talking to a whale because of this. When we're lucid however, the PFC is active once again.

Yeah don't worry about it, it's completely normal to accept strange stuff in a dream.
For example I had a non lucid last night where I bought a Lamborghini.

It's completely normal :) this is what lucid dreaming is for~

+1 to Auron for big words XD

When you are sleeping, your brain is very active (especially during the R.E.M phase) however the part of your brain which is responsible for processing logic, is very dormant and inactive, which is why you accept is as normal, and when you wake up, so does your logic and then it kicks in and says "Dayum" :)

However, with training and reality checks this improves and the use of dreamsigns can be an important tool here, If you keep seeing pink elephants in a lot of dreams, then that's a dreamsign, when you can get your brain and logical thinking to acknowledge there is a pink elephant and that's not normal... then BAM... Lucid.